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diff --git a/old/54276-0.txt b/old/54276-0.txt deleted file mode 100644 index 877144c..0000000 --- a/old/54276-0.txt +++ /dev/null @@ -1,4269 +0,0 @@ -The Project Gutenberg EBook of Physiology and histology of the Cubomedusæ, by -Edward William Berger - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org/license - - -Title: Physiology and histology of the Cubomedusæ - including Dr. F.S. Conant's notes on the physiology - -Author: Edward William Berger - -Contributor: Franklin Story Conant - -Release Date: March 3, 2017 [EBook #54276] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK CUBOMEDUSAE *** - - - - -Produced by Donald Cummings, Bryan Ness and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - - - - - - - - - - Memoirs from the Biological Laboratory - OF THE - JOHNS HOPKINS UNIVERSITY - IV, 4 - WILLIAM K. BROOKS, EDITOR - - PHYSIOLOGY AND HISTOLOGY - OF - THE CUBOMEDUSÆ - - INCLUDING - - DR. F. S. CONANT’S NOTES ON THE PHYSIOLOGY - - A DISSERTATION PRESENTED TO THE BOARD OF UNIVERSITY STUDIES - OF THE JOHNS HOPKINS UNIVERSITY - FOR THE DEGREE OF DOCTOR OF PHILOSOPHY - - BY - E. W. BERGER - - BALTIMORE - THE JOHNS HOPKINS PRESS - 1900 - - [Illustration] - - PRINTED BY - The Lord Baltimore Press - THE FRIEDENWALD COMPANY - BALTIMORE, MD., U.S.A. - - - - -This Memoir is a continuation of the work upon the Cubomedusæ which was -begun by the late Dr. FRANKLIN STORY CONANT, and it contains his notes -of physiological experiments, as well as new results which have been -obtained by Dr. E. W. BERGER from the study of material which had been -collected by Dr. CONANT, who had hoped to make it the object of further -study. - -In order that this work may be made public as a continuation of Dr. -CONANT’S researches, his sister, GRACE WILBUR CONANT, has, with the -coöperation of other members of his family, made an adequate and generous -provision for its publication. - -For this gift, which is at once a contribution to science and a memorial -of an able and promising investigator, lately student and fellow in -this institution, the Johns Hopkins University returns its grateful -acknowledgments. - - DANIEL C. GILMAN, _President_. - W. K. BROOKS, _Professor of Zoölogy_. - - - - -CONTENTS. - - - PAGE - INTRODUCTION. - - History 1 - - Epitome of Anatomy 2 - - PHYSIOLOGICAL. - - CHARYBDEA. - - Light and Darkness 5 - - Concretions 8 - - Sensory Clubs 9 - - Velarium and Frenula 11 - - Pedalia, Interradial Ganglia, Tentacles 12 - - Stomach, Suspensoria, Proboscis, Subumbrella 13 - - Margin, Radial Ganglia, Nerve 15 - - Stimulation 17 - - Activity of Charybdea 17 - - Temperature 17 - - Food and Feeding 18 - - Occurrence of Charybdea 18 - - AURELIA AND POLYCLONIA (_Cassiopœa_) 19 - - SUMMARY 22 - - DR. CONANT’S NOTES. - - CHARYBDEA. - - Light and Darkness 24 - - Sensory Clubs 26 - - Nerve 29 - - Side, Subumbrella 30 - - Pedalia, Velarium, Ganglia 31 - - Tentacles 32 - - Proboscis, Stomach, Phacelli 33 - - Temperature 33 - - Food and Feeding 33 - - Occurrence of Charybdea 33 - - Activity of Charybdea 34 - - AURELIA AND POLYCLONIA 35 - - CASSIOPŒA 39 - - AURELIA 39 - - HISTOLOGICAL. - - Method 40 - - Anatomy 41 - - Distal Complex Eye-- - - General 41 - - Cornea 42 - - The Lens 42 - - The Capsule 44 - - The Retina 45 - - (a) The Prism Cells 46 - - (b) The Pyramid Cells 48 - - (c) The Long Pigment Cells 50 - - (d) Subretinal Nerve Tissue 53 - - (e) Discussion of Literature 53 - - (f) Function of the Retinal Cells, Patten’s Theory, and - further Literature 56 - - The Proximal Complex Eye 60 - - The Simple Eyes 61 - - Lithocyst and Concretion 63 - - The Epithelium of the Clubs 64 - - Network and Multipolar Ganglion Cells 67 - - The Nerve Tissue 67 - - The Supporting Lamella 68 - - Epithelium of Ampulla and Floating Cells 68 - - The Endothelium of the Peduncle 73 - - The Tentacles and Pedalia-- - - The Ectoderm 74 - - (a) Thread Cells 74 - - (b) Muscle Fibers 74 - - (c) Ganglion Cell 75 - - The Endoderm 75 - - SUMMARY 77 - - LITERATURE 78 - - REFERENCE LETTERS 80 - - DESCRIPTION OF FIGURES 81 - - - - -INTRODUCTION. - - -This paper may be regarded as a continuation of the Cubomedusan studies -pursued by Dr. F. S. Conant while in Jamaica, in 1896 and 1897, with the -Johns Hopkins Marine Laboratory. His systematic and anatomical results -have since been published as his Dissertation (“The Cubomedusæ”) by this -University. Conant described this paper as Part I, hoping soon to add -a second part on the physiology and the embryology, for which he had -some notes and material at hand. Returning, however, to Jamaica with the -laboratory, in 1897, he continued his physiological experiments, and -preserved material for histological purposes. Upon the untimely death -of Conant, his material and notes were placed in my hands by Professor -Brooks, to whom I here take the opportunity of expressing my appreciation -and sincere thanks for the honor thus conferred and for the many favors -received. - -In this paper I shall note at some length Conant’s physiological results -and append his notes. I shall also add my results on the histology of -the eyes and the sensory clubs in general, with some few facts on the -histology of the tentacles. The embryology will be reserved for a future -paper. - -The forms used in the physiological experiments were Charybdea Xaymacana, -one of the two species (see Literature V, a and b) first found and -described by Conant; Aurelia aurita; Polyclonia and Cassiopœa. The -greater number of Conant’s notes are on Charybdea, and were left by him -just as taken at the time of experimenting. Many of these notes are -highly interesting and in the main fit in well with Romanes’[I] and -Eimer’s[IV] results. - -Dr. Conant’s work on Charybdea, in 1897, was wholly done at Port Antonio, -Jamaica. At first Conant had only varying success in obtaining Charybdea, -scouring the harbor and neighboring water at all hours, only to obtain -but few specimens. It was on the forenoon of August 7th, while we were -dredging at the head of East Harbor with a steam launch, that many -Charybdeæ were brought up in the dredge. This gave Conant a clue to -their whereabouts and to the means of obtaining them, and from that time -on he was able to obtain them in abundance. His first physiological -experiments were begun on August 4th and continued thereafter at -intervals of several days until his departure from Jamaica on September -6th. - -Dr. Conant usually performed his experiments during the second half -of the forenoon, after the animals had stood for a few hours in the -laboratory. - -The building that was rented at Port Antonio for a laboratory had, in -the basement, a photographer’s dark-room, which was of great service to -Conant in his experiments. - -The experiments on Aurelia, in 1897, were also performed at Port Antonio, -between August 6th and 9th. The experiments on Cassiopœa were probably -made at Port Antonio, where specimens were occasionally obtained. - -The notes on Aurelia and Polyclonia, in 1896, were taken at Port -Henderson, between May 12th and June 27th. - -In his notes Conant speaks of Polyclonia and Cassiopœa. It is at present -undetermined whether he really had both forms or whether he uses the two -names for the same form. It seems likely that in 1896 he thought the -form to be Polyclonia, while for some reason, in 1897, he supposed it to -be Cassiopœa. I have examined several specimens of these medusæ brought -from Port Antonio and find that they all have twelve marginal bodies and -twenty-four radial canals, according to which (V, Haeckel’s System), -they should be Polyclonia. Conant, however, speaks of removing sixteen -marginal bodies, which seems to indicate that he had Cassiopœa. A careful -classification of this form of medusæ found about Jamaica seems to be a -desideratum. I suppose, however, that for our purpose in this paper it -will make little difference which name is used, the two forms being so -similar in form and structure. I have, therefore, decided to retain both -the names used by Conant. - -For the complete anatomy of Charybdea the reader is referred to Dr. -Conant’s dissertation, “The Cubomedusæ” (8b), or the _Johns Hopkins -University Circulars_ (8a), both published by the Johns Hopkins Press. -But, for the convenience of those who may be less familiar with -Cubomedusan anatomy, the following brief summary of the anatomy of -Charybdea is given: - -The Cubomedusæ, as the name implies, approximate cubes, with their -tentacles (four in Charybdea) arranged at the four corners of the lower -face of the cube. These tentacles are said to lie in the interradii. -Half way between any two points of attachment of the pedalia (the basal -portions of the tentacles) and a little above the margin of the bell -(cube), in a niche, hang the sensory clubs, one on each side, four in -all. Each sensory club hangs in a niche of the exumbrella and is attached -by a small peduncle whose axial canal is in connection with one of -the four stomach-pockets and in the club proper forms an ampulla-like -enlargement. - -Each club is said to lie in a perradius, and, like the tentacles, belongs -to the subumbrella. This is shown by the course of the vascular lamellæ, -bands of cells that, stretching through the jelly from the endoderm to -the ectoderm all around the margin, form the line of division between -sub- and exumbrella. - -Each club has six eyes. Two of these on the middle line of the club -facing inwards are called the proximal and distal complex eyes, to -distinguish them from the four simple eyes that are disposed laterally, -two on each side of the line of the two complex eyes. All of these eyes -look inwards into the bell cavity through a thin transparent membrane -of the subumbrella. Besides the eyes and the ampulla already mentioned, -a concretion fills the lowermost part of the club, and a group of large -cells, having a network-like structure and called network cells by -Conant, fill the uppermost part of the club between the proximal complex -eye and the attachment of the club to its peduncle (Plate II, Fig. 13). -What is evidently nerve tissue, fibers and ganglion cells, fills the rest -of the club, with two groups of large ganglion cells disposed laterally -from the network cells. A sensory (flagellate) epithelium covers the club. - -Most Cubomedusæ, among them Charybdea, have a velarium (comparable to the -velum of the Hydromedusæ), a membrane of tissue that extends inwards at -right angles all around the margin. This velarium, like a velum, has a -central opening through which the water is expelled from the bell-cavity -when the animal pulsates. In the perradii and in the angle between the -velarium and the body wall, are the frenula, which give support to -the velarium much like brackets support a shelf, except that here the -brackets are above the shelf instead of below. - -In the upper part of the bell is the stomach, with the phacelli in its -interradii, and continued ventrally into the manubrium, or the proboscis. -The cavity of the stomach is continued in the perradii through the four -gastric ostia into the four stomach pockets, which occupy the sides of -the bell and extend to the margin. Immediately below the gastric ostia, -and in the bell cavity, are the suspensoria, one in each perradius. -These support the floor of the stomach much as the frenula support the -velarium, except that the suspensoria are placed under the shelf (to -continue Conant’s figure) and not above it as are the frenula. - -A nerve ring, underneath the epithelium of the subumbrella, passes from -near the origin of each pedalium at the margin to the origin of the -peduncles of the sensory clubs, a little above the margin, giving off a -branch to each club. Eight ganglia are found in the course of this nerve. -The four pedal ganglia lie near the bases of the pedalia, and are hence -interradial; the four radial ganglia lie near the bases of the peduncles -of the clubs, and are perradial. A small nerve, radial nerve, can be -traced a short distance upwards from each radial ganglion. Underlying -the epithelium of the frenula and the suspensoria are ganglion cells and -nerve fibers in larger numbers than elsewhere (excepting the ganglia -mentioned) in the subumbrella. Otherwise, ganglion cells and nerve fibers -underlie the epithelium of the subumbrella, including the inner surface -of the velarium, as also do muscle fibers, except in the perradii and in -the region of the nerve, where the latter become interrupted. - - - - -PHYSIOLOGICAL. - -CHARYBDEA. - - -_Light and Darkness_--Experiments 1-9, 10, 33, 34.--As already stated -in the Introduction, a part of Conant’s experiments were performed -in a photographer’s dark-room, with the animals in a deep glass jar. -In the dark a fair proportion of the animals became nearly quiescent -on the bottom, but upon lighting a lamp many started up immediately, -while others took a longer time to come to the surface and swim. These -experiments were tried a number of times and on different occasions with -very similar results. Some medusæ, however, tried immediately after -being brought in, seemed not to react so well upon being placed in the -dark-room, nor would they become quiescent. This, probably, was due to -the fact that the animals had not yet recovered from the effects of being -caught and placed in new surroundings. (Experiments 1, 2, 3.) - -Other experiments (4-8, 33, 34) were tried by carrying the jar with the -animals from the weaker light of a room into the more intense light of -outdoors or into direct sunlight. The usual result was an inhibition of -pulsation and a settling to the bottom, while the medusæ immediately -became active again upon returning with them to the room. These results -were so marked that no doubts can be entertained as to their cause, -though some exceptions occurred in which animals placed in the sun -continued to swim on the surface or soon recovered pulsation. In some -experiments, too, no animals responded to the inhibitory stimulus of the -brighter light or all very soon recovered. (See, however, Temperature.) - -Reducing the light by placing a coat over the jar produced the same -effect in some experiments (8, 9, 10) as did reducing the light in other -ways, while removing the coat produced the same effect as exposure to -brighter light. In these instances it appears to be the transition from -weaker to stronger light that inhibits pulsation, rather than the actual -intensity of the light; and _vice versa_. It must be noted, too, that -when left for some time in any one place the animals changed, some -coming to the surface and others going to the bottom. - -These experiments show beyond doubt that Charybdea is sensitive to -light, and that it is moderate light that stimulates the animals to -activity, while darkness and strong light inhibit activity. While the -individual exceptions, as Conant himself suggests, are well explained -on the supposition of individual diversity, yet it appears that other -conditions, such as the time of day, temperature, etc., may have been -responsible for some of the exceptional experiments in which no animals -responded as expected. - -While light of any intensity seems to have stimulated Romanes’[I] Sarsia -and Tiaropsis (Hydromedusæ) to activity, we note that it is moderate -light that stimulates Charybdea. This fact is evidently correlated with -the circumstance that Charybdea usually lives upon or near the bottom. - -It may further be added in regard to Romanes’ Tiaropsis polydiademata, -that when it was suddenly exposed to light it went into a spasm -preceded by a long latent period during which there was a “summation of -stimulating influence” in the ganglia. Sarsiæ would congregate toward -the source of light and in general were more active in light than in the -dark, while sudden darkness often inhibited a swimming bout. Romanes -proves for Sarsia that the marginal bodies are the seat of luminous -stimulation and that it is the light rays and not heat rays that -stimulate. He also remarks that he has obtained similar results on the -covered-eyed (Scyphomedusæ) medusæ, namely, that they respond to luminous -stimulation. - -It may here be of interest to note a few observations made by myself at -Wood’s Holl, Mass., on a beautiful Olindiad, which is abundant in the -Eelpond at the above place. I found that in a room, in the ordinary light -of evening, the animals swam actively; but the moment the electric light -was turned on they stopped swimming and settled to the bottom or attached -themselves to a branch of some weed or stem suspended in the water. -This was the result in every trial. It is found, further, to be little -active during the brighter parts of the day, when one must dip quite deep -with a net in order to obtain it. A similar observation is also made by -Murbach[II], who further states that this medusa may be deceived into -laying its eggs by placing it in the dark. - -One cannot help but remark how analogous is the behavior of medusæ, in -respect to light and darkness, to the behavior of many of the higher -animals,--and medusæ are among the most lowly organized of the animal -creation. - -Were one to conclude from the behavior of Charybdea in light and darkness -in the laboratory, that it remained on or near the bottom in the daytime -but became more active near or at the surface evenings, nights and early -mornings, one would probably not be far from the truth. Dr. Conant, -while towing near the bottom with a weighted net, in water four to five -feet (1.2-1.5 m.) deep not far from shore and deeper farther out, found -Charybdea in abundance mornings and afternoons, but very few in the -evening. In the evening some few were usually taken in the surface tow. -(See Introduction, Occurrence and Activity.) - -Again, who knows but that Charybdea is active during the day, on the -bottom where it was dredged (the light there would only be moderate), -and quiet at night. This supposition would seem to be true, at least, -for those forms of Cubomedusæ that live in deep water. We can hardly -suppose that they should regularly rise to the surface from great depths -and become active. This much we do know that bright light inhibits -Charybdea’s activities, while it probably would not be active in perfect -darkness. - -I do not know just what interpretation to put upon Conant’s finding -Charybdea at Port Henderson at the surface during the early part of the -forenoon, before the sea-breeze roughened the water (“Cubomedusæ” p. 7). -This fact hardly fits in with my conclusions above. Perhaps Charybdea’s -habits vary with its habitat. - -Finally, while I find no experimental evidence in Conant’s notes about -what parts of Charybdea are sensitive to light, yet it would seem -preposterous, from histological evidence and from Romanes’ results on -Sarsia, to doubt that the eyes of the marginal bodies are the seat of -this stimulation. - -Dr. Conant further experimented by cutting off certain organs and parts -from the Cubomedusan bell. These excisions consisted chiefly in cutting -out the concretions of the sensory clubs, cutting off the whole club, -eliminating a part or whole of the margin and the velarium, cutting the -bell into sectors, excising the stomach and parts connected with it, and -other parts. - - -_Concretions_--Experiments 10, 11.--The four concretions were removed -from each of four animals. Two of these (Experiments 10, and another (X), -not appended, to save space) seemed to be little if at all affected by -the operation. One of the two (10) swam actively, at first up and down -more changeably than those intact, but later mostly near the surface. -The other one also swam actively and showed nothing to indicate weakened -sense-perception. The other two (11) did not stand the operation well, as -Conant remarks, and immediately went to the bottom, where they remained, -one swimming, while eight hours later one was still in good condition. - -Several attempts with stronger light by removing the coat from the -jar made no difference in the behavior of 10; it continued to swim as -heretofore. Upon a final trial, however, with removing the coat, it went -to the bottom, thus showing a possible reaction to light; but when next -seen it was keeping to the bottom. - -That the concretions should function as organs of light sensation, as -the first of the above animals might seem to indicate, I believe is out -of the question.[a] The fact, too, that this same animal (10), together -with another (X), swam actively, immediately changing their course upon -coming to the surface, in reality behaving quite as normal animals, -hardly permits us to conclude from the behavior of the other two (11) -that the concretions function directly as organs of equilibrium or space -relations. May these concretions not function simply as weights for -keeping the sensory clubs with their eyes properly suspended? Since these -concretions lie at the lowermost part of the clubs and in closed sacs and -unsupported by cilia, it would seem that the above suggestion as to their -being weights is not improbable. Direct observation (Experiment 20) by -Conant shows, furthermore, that the clubs always hang with a tendency for -the concretions to be lowermost, regardless of the position of the animal. - -Again, while they may function as weights, as just explained, the fact -that the epithelium of the clubs is flagellated (a flagellum, continued -as a nerve fiber, to each cell--see Histology), the supposition lies -near that these flagella are the ones influenced by the concretions as -the clubs bear against one side of the sensory niche or the other. A -somewhat similar view seems to be held by other observers and is noted by -Lang in his text-book (“The outer epithelium of the auditory body carries -the auditory hairs”). It seems, then, that in functioning as weights for -suspending the clubs, they may also serve at the same time for making the -pressure of the club against the niche greater than if they were absent, -and thus in part serve in equilibrium. On this supposition we should -expect, furthermore, that after the removal of the concretions the animal -would be little, if at all, affected, since the clubs themselves, without -the concretions, would still be of sufficient weight to be influenced -by gravity and thus to bear against the walls of the sensory niche. It -must be noted, however, that Conant’s experiments upon equilibration in -Charybdea are negative. Also, that Charybdea has any auditory sense is -negatived by two attempts of Conant’s with a violin--one attempt with the -violin near the animals, and another with it in contact with the dish. -(From an unpublished note.) Hence, some other word such as sensory or -equilibrating should perhaps be substituted for “auditory” in the above -quotation. - -Removing the concretions from Aurelia gave negative results very similar -to those on Charybdea. (Experiment 42.) - - -_Sensory Clubs_--Experiments 12-19, 20, 24.--The entire sensory clubs -were removed from a number of animals. A paralysis of pulsation followed -by a rapid recovery was the usual result. In some instances, however, -there was no paralysis, while in others no recovery followed paralysis. -This is true in a general way whether one club only or all were removed. -While no permanent paralysis followed the removal of one or two clubs, -yet permanent paralysis did occur after the removal of a third club, as, -of course, also after the removal of a fourth. It is evident, too, that -as the removal of the clubs progressed recovery seemed to be weaker after -each cutting, except in one case when pulsation seemed to be quickened -after the removal of a second club. The pulsations after recovery seemed -to be not so strong and regular, often quite feeble, and in one instance -in groups. Pieces of tissue with a club attached and pulsating regularly, -ceased pulsating after removal of the club, in one instance, however, -still giving occasional contractions. - -These results are quite the same as those of Romanes[I] on Aurelia, -Cyanæa, etc., and of Eimer[IV] on Aurelia, Rhizostoma, Cotylorhyza, -etc.[b] In these forms Romanes sometimes obtained complete paralysis -after the removal of the sensory clubs only, as also after the removal of -the whole margin, though this was not marked in Aurelia. In Cyanæa and -other forms motor centers seemed to be more abundant than in Aurelia, -so that paralysis was oftener followed by recovery. He concludes that -while the principal motor centers reside in the lithocysts, other centers -doubtless exist that may function vicariously, but that the centers of -the margin are more definitely limited to the marginal bodies in the -Scyphomedusæ than in the Hydromedusæ, in which the whole margin seems -to be replete with centers. He feels positive, furthermore, that no -motor centers exist in Aurelia’s margin outside of the marginal bodies -(lithocysts). Eimer’s results are essentially the same as Romanes’, so -that for a more detailed comparison of the two, Romanes’ works should be -consulted. - -Romanes’ conclusion for the Hydromedusæ is that the motor centers are -not so definitely localized in the marginal bodies, but in the margin -generally, the excision of the marginal bodies alone producing only -partial paralysis, as would also the removal of the margin from between -the marginal bodies, but not so marked. For the Hydromedusæ he concludes, -then, that all the centers of spontaneity are definitely localized in -the margin, but not limited to the marginal bodies. To this he mentions -one exception, namely, _Staurophora laciniata_, in which another center -is found near the margin and two others in two opposite arms of the -proboscis. - -I made the remark in an abstract (VI) on Conant’s notes that Romanes did -not obtain recovery of pulsation after removal of all the lithocysts in -Aurelia. As noted above, he did obtain recovery, so that Conant’s results -on Charybdea and also Aurelia (see Polyclonia and Aurelia) are quite in -agreement with Romanes. - -The paralysis following the removal of the clubs in Charybdea is -evidently, primarily, the result of a loss of a part of its nervous -mechanism (motor centers), and, secondarily, of nervous shock, and -points to the existence of a definite nervous mechanism in the clubs. -The histological evidence is here, as usual, corroborative of the -physiological. - -Another interesting phenomenon observed after the removal of one or -all of the clubs was the strange behavior of the proboscis. This would -reach from side to side, expanding and contracting its lips as if -trying to grasp something. This behavior is very similar to that of the -proboscis of _Tiaropsis indicans_ when Romanes stimulated any part of its -subumbrella, or of _Limnocodium sorbii_, a little fresh-water medusa, -when he stimulated its margin or the region of the radial canals. (Ib., -p. 242.) - -I may add that I observed a very similar movement of the proboscis of the -Olindiad, before mentioned. When I pulled off pieces of its gonads by -means of quick jerks, with a small forceps, it would continually reach -toward the injured part of its subumbrella. This medusa is generally -quite active with its proboscis and can occasionally be seen to reach -with it. - -Romanes states in one place that the proboscis is not affected by the -excision of the margin. This is evidently not the case in Charybdea, -in which excision of the sensory clubs (which really belong to the -margin--see “Cubomedusæ”) decidedly stimulated the proboscis to active -movements. This, furthermore, points to the marginal bodies as being -organs of considerable importance in giving information in the life of -Charybdea. In Romanes’ Sarsia and other medusæ, however, the proboscis -did respond to the stimulation of the tentacles and the marginal bodies, -as also would the bell respond to a stimulation of the proboscis -(manubrium), thus showing a reflex nervous connection between these -regions of the bell, similar to that described for Charybdea. - - -_Velarium and Frenula_--Experiments 18, 29, 30, 41c.--“The power of -originating contractions” to use Conant’s own words, “evidently resides -in the velarium or in ganglion cells of the frenula, just as it does -in the proboscis and the floor of the stomach.” Isolated pieces of the -velarium contracted by themselves as did the whole velarium when all -other tissue had been removed. An isolated velarium with the margin and -the pedalia attached gave irregular contractions. When the pedalia with -the _interradial ganglia_ were removed it still contracted; and when all -the other tissue was cut off contractions continued. - -Cutting the velarium caused the _pedalia_ to be strongly contracted -inwards so that the tentacles were brought inside the bell. Cutting away -the velarium did not interfere with the pulsations of the bell, but -progress was much retarded. - -Cutting the frenula caused the pedalia to contract but seemed not to -affect the ability to swim. Comparing the velarium of the Cubomedusæ -with the velum of the Hydromedusæ, I recall no observations similar -to the ones here noted, though it seems that the two may have quite -similar functions. It seems somewhat probable that the velum, and also -the velarium, may function in obtaining food,--and this besides their -function in swimming. Their probable function in swimming, as is well -known, is evidently to narrow the mouth of the bell and thus to cause -the water to be forced out in a smaller but more rapid stream, giving -the animal a steady and more prolonged movement through the water at -every contraction of the bell. In regard to taking food, I observed that -a small crustacean, in the process of being swallowed by an Olindiad, -seemed to be held by the velum being firmly contracted about it while -the proboscis was working itself over the crustacean. It would seem, -furthermore, that my supposition is supported for Charybdea by the fact -that the pedalia and tentacles were contracted so as to be brought inside -the bell when the velarium was cut. The stimulus of cutting the velarium -may be comparable to a stimulus from some object touching it, and thus -cause the pedalia and tentacles to come reflexly to aid in capturing or -holding the object, a fish, crustacean, or such, to be captured. - - -_Pedalia, Interradial Ganglia, Tentacles_--Experiments 15, 23, 27-31, -41b.--When the pedalia were removed, the power of the animal to guide -itself was completely gone. When one pedalium was cut the others -contracted, while stroking the outer edge of the pedalia, touching the -sensory clubs, or sharply pricking the subumbrella, often produced the -same result. (See also Nerve.) The upper part of the subumbrella seemed -not so sensitive and more seldom produced the reflex of the pedalia, -while the base of the stomach did not give it at all. Stroking the outer -edge of the pedalia of _Tripedalia cystophora_, the second of the two -species of Cubomedusæ described by Conant, also caused the pedalia to -be contracted inwards. I may note here that the muscle fibers under the -ectoderm of the pedalia are specially well developed at and near the -inner and outer edges, both in Charybdea and Tripedalia. On the flattened -sides of the pedalia the muscle fibers are fewer. - -When the pedalia were cut off far enough up to remove the interradial -ganglia, coördination was not affected and the animal could pulsate well -enough but with little progress. (See above under Velarium and Frenula.) - -An isolated tentacle is capable of squirming contractions, and when -stimulated at either end, it would contract wholly or in part only. - -The pedalia, then, it would seem, serve also as a steering apparatus, for -which they are admirably fitted, considering their blade-like thinness. - -Considering, now, the reflexes noted under this head and the preceding -one, we find that there is an intimate nervous connection between the -velarium and frenula, subumbrella, sensory clubs, nerve, and a single -pedalium, on the one hand, and the pedalia on the other hand. This -is born out fully, furthermore, by the histological evidence--(See -Introduction and “Cubomedusæ”). Considering the subumbral plexus of -ganglion cells and fibers, including the velarium and the frenula, which -is in connection with the nerve ring and this again with the sensory -clubs and the interradial ganglia at the bases of the pedalia, we have -a basis for these reflexes. While Conant failed to demonstrate nerves -(“Cubomedusæ”) from the interradial ganglia to the pedalia, yet, that a -nervous connection exists between the pedalia and the bell is well shown -by his physiological experiments. I have, furthermore, demonstrated -ganglion cells under the ectoderm of the tentacles (see Histology). - -Romanes obtained quite similar results in the Hydromedusæ. He found -that when a tentacle of Sarsia was slightly stimulated, it alone would -contract, but when it was more strongly stimulated the other tentacles -also would respond as also the manubrium. I find no evidence in Conant’s -notes of any such response of the manubrium of Charybdea, except when the -clubs were cut off. - -The reflex obtained on stimulating the subumbrella of Charybdea, when -the pedalia would contract, is somewhat different from that obtained by -Romanes, who found that the most sensitive part of the subumbrella in -producing a reflex of the margin was at the junction of the manubrium -to the bell and that the subumbrella below this point did not give the -reflex. - -_Stomach, Suspensoria, Proboscis, Subumbrella_--Experiments 12, 18, 19, -24-26, 29, 31.--The proboscis and the stomach with the phacelli when cut -out, contracted with or without the lips removed. The isolated lips also -contracted (twitched). - -Pieces of the sides connected only with the stomach and suspensoria, or -with the margin (Experiment 47 (?)) twitched spontaneously, but seldom -did so when these were removed. In one instance the whole side was cut -out so as to exclude the radial ganglion but still connected with a -portion of the suspensorium. This pulsated, or contracted, but on being -halved transversely, the lower half ceased to contract while the upper -half connected with the suspensorium, continued to contract. - -Cutting off the whole stomach end of the animal excited to very rapid -pulsations of the remaining part, with the stream of water stronger out -the aboral end than past the velarium. - -Conant says, “It seems I get no good evidence of the subumbrella without -connection with special nerve centers being able to contract by itself.” -The piece in which he did get contractions he suspects may have been -intimately associated with some part of the frenula or the suspensoria. -In Polyclonia no such doubt exists, for small pieces of subumbrella -were seen to contract. A small piece of subumbrella of Charybdea with a -sensory club attached could contract by itself. - -From the above it would seem that a center capable of inciting to -contractions resided in the suspensoria as well as in the sensory -clubs, and this may be one of the centers that becomes potent upon the -removal of the clubs. This is further supported by Conant’s observation -(Introduction and “Cubomedusæ”) that an extra large number of ganglion -cells is found under the epithelium of the suspensoria. A somewhat -similarly located center of spontaneity described by Romanes for -_Staurophora laciniata_ (Hydromedusa) has already been noted. - -As to the rapid pulsations of the bell after cutting out the stomach -end, this also is similar to Romanes’ results on Aurelia and other -Scyphomedusæ, when he cut off parts of the manubrium or an aboral ring -out of the bell. In these instances, however, Romanes soon obtained -a slackening of the rhythm following the temporary acceleration. The -temporary acceleration he attributes to the stimulus of cutting, and the -slackening to a lack of some afferent stimulus from the removed tissue. -Conant obtained the same results on Polyclonia by removing the oral arms -(see Polyclonia) but says nothing about a slackening of the rhythm in -Charybdea. I believe the increased rhythm in Charybdea was in part due to -the decreased amount of labor necessary to force the water out of two -openings instead of one, namely, past the velarium. Just how much this -observation bears upon Romanes’ theory of rhythmic contraction, that the -rhythm is due to an alternate exhaustion and recovery of the contractile -tissue, as opposed to the ganglionic theory of rhythm of physiologists, -one does not wish to speculate much. Yet, I feel that the observation -rather supports this theory. The tissue having to do less work, would -become less exhausted at each contraction and require less time for -recovery and hence have a more rapid rhythm. - -I here sum up Romanes’ theory in a few words. The ganglia liberate a -constant and comparatively weak stimulus, one perhaps about minimal. This -stimulus sets off the contractile tissue; but as the tissue contracts -and becomes exhausted the constant stimulus becomes, in relation to it, -sub-minimal, and it does not contract again until it has recovered and -the stimulus is again strong enough to set it off. The ganglionic theory -of rhythmic contraction supposes that the ganglia liberate stimuli to -the contractile tissue at successive intervals. Romanes had this theory -suggested to him by the rhythmic contractions he succeeded in obtaining -by subjecting deganglionated bells to a continuous but weak faradic -stimulus, or by placing them into weakly acidulated water, or into 5 per -cent. glycerine. Romanes claims that his theory better explains muscular -tonus and the contraction of involuntary muscle. He does not, however, -hold this theory to the exclusion of the ganglionic theory, since only -too often does he speak in terms of the latter. He further brings in his -support the fact that the frog’s tongue, in which no ganglia have been -demonstrated, can be made to contract rhythmically when subjected to a -weak and continuous stimulus. He also calls attention to the rhythmic -contractions seen in the Protozoa, the snail’s heart, etc. Finally, -physiologists are much inclined to explain the rhythmic contraction of -the heart and other involuntary muscles, in part, at least, as due to a -property of the contractile tissue. - - -_Margin, Radial Ganglia, Nerve_--Experiments 18, 21-23, 30.--Complete -removal of the margin did not stop pulsation; but the removal of the -radial ganglia stopped it permanently. While this experiment seems to -have been tried only once, yet, taking into consideration the results of -other operations, it would seem that the principal centers of spontaneity -reside in these ganglia. (It should here be remembered that the -interradial ganglia were probably removed at the removing of the margin.) - -Cutting the nerve in the eight adradii caused the _pedalia_ to bend -inwards at right angles to their normal position but did not in the least -affect the coördination of the sides. When, however, the sides were cut -in the eight adradii to the base of the stomach, coördination for the -main part ceased, and each side pulsated in its own rhythm. - -I have said that the principal centers of spontaneity reside in the -radial ganglia. Upon further thought this hardly seems warranted. No -doubt, among the principal motor centers must be placed the ganglionic -masses of the clubs, and the radial ganglia, together with the homologous -interradial ganglia, represent centers of equal value. I speak of these -two sets of ganglia as homologous, since strictly speaking, they both -belong to the margin, and the clubs at whose bases they lie probably -represent modified tentacles. Conant’s experiments leave us in the -dark as to the function of these ganglia. Next in order, it would -seem, are the ganglion cells in the suspensoria, as is suggested by -the contractions of an isolated side with a portion of a suspensorium -attached. (See previous head.) While we have seen that the frenula and -the velarium can contract by themselves, yet, I find no evidence that -these can impart their contractions to any adjacent tissue. - -Conant’s results on cutting the nerve eight times and then continuing the -cuts to the base of the stomach are quite the same as Romanes and Eimer -obtained upon Aurelia. Romanes, however, concludes that in his Sarsia, -Tiaropsis, etc., coördination was broken when only short incisions were -made in the margin. Charybdea appears, then, to agree with Aurelia rather -than with the Hydromedusæ. Yet, since Romanes at first obtained similar -results to those of Charybdea on Sarsia, but on further experimenting -concluded that coördination had really been destroyed at the first -cutting, we cannot speak with certainty that coördination had not been -destroyed in Charybdea before the cuts had been continued to the base of -the stomach. I say not with certainty, because the injury to the bell -being slight, coördination may have been maintained on the principle of -a simultaneously (simultaneous for the octants) alternate exhaustion and -recovery of the contractile tissue on the principle of Romanes’ theory. - - -_Stimulation._--Romanes found when he stimulated a deganglionated bell -of a Hydromedusa, that it responded by a single contraction, while that -of a Scyphomedusa responded with several quite rhythmic contractions. -Charybdea in this respect agrees with the Scyphomedusæ. Romanes’ results -were also verified on Aurelia. (Experiments 12c, 15, 50, 51.) - - -_Activity of Charybdea._--In speaking of the activity of Charybdea, I -cannot do better than refer the reader to the notes. (Experiment 41.) -Conant remarks in his dissertation what an active swimmer Charybdea is, -and this is further borne out by his later observations. - - -_Temperature._--Ice in the water seemed to have no effect, except when -held against an animal, when a slowing of pulsation followed in a few -instances. On some pulsating actively in the sun the temperature of the -water was found to be 92° F. (Experiments 33-35.) - -Conant does not tell us how cold the water became when he placed ice in -it, but judging from his results, it seems that he might have obtained -a decided slowing of pulsation if the water in which the medusæ swam -had been permitted to approach anywhere near the freezing point, say -35-40° F. Romanes obtained decided slowing of pulsation, and even -complete inhibition, on a bell of Aurelia, as also a lengthening of the -latent period on some strips cut from a bell of Aurelia, by lowering -the temperature of the water. Replacing Aurelia in warmer water had -the effect of immediate recovery and increased rhythm. In Aurelia, -raising the temperature increased the rhythm but diminished it when the -temperature of the water became 70-80° F. After a slowing of pulsation -due to such a rise of temperature, it would not quicken again when the -animal was placed in water of its normal temperature. Romanes explains -this by supposing that the tissue of the medusa had been permanently -injured by the abnormally high temperature. It would be interesting to -observe how the tropical Aurelia behaved under such treatment, seeing -that Charybdea pulsated actively and without apparent injury in water at -92° F. _Limnocodium_, noted by Romanes, and probably a tropical species, -lived happily in water at 85° F. in the lily house of the Royal Botanical -Society. The temperature of the water could be raised to 100° F. before -it proved fatal to this medusa. Such facts point to a decided difference -in the constitution of the protoplasm of tropical and temperate medusæ. -Romanes’ Sarsia became frantic when placed in milk-warm water. - -While writing the above, I was led to wonder whether the temperature -of the water may not have been the stimulating influence in those -experiments on light (previously noted) in which the medusæ continued to -swim actively in the sunlight. - - -_Food and Feeding._--See Experiment 36. - -I again make note of a few observations made by myself on the Olindiad. -A crustacean became entangled in the tentacles of a medusa; apparently -this wished to retain it, for the proboscis reached in the direction -of the crustacean, which, however, got away. I then placed, by means -of a needle, another small crustacean against one of the tentacles. -This was seized but not retained, for the animal pulsated and it was -washed away by the water. Twice I saw a good-sized crustacean in the -proboscis. In one instance the velum appeared to hold the part of the -crustacean not yet in the proboscis. I noticed another with a crustacean -wholly in the proboscis, which was much lengthened out, the upper part -of the crustacean being in the stomach. The next morning the crustacean -was wholly in the stomach and the proboscis normal. At 5.30 P. M. the -crustacean was ejected, nothing but the shell and some rubbish remaining. - -These medusæ seem to pay no attention to being touched by one of their -kind, except to give a pulsation or two. - -The proboscis appears very “intelligent” in its actions.[c] First, some -of the tentacles can be seen to contract and to bend inwards, then the -side next the tentacles contracts and the proboscis is seen to reach in -that direction. I could not see, however, what the irritant was. - - -_Occurrence of Charybdea_--Experiments 37-40.--Dr. Conant’s remarks -(“Cubomedusæ”) on the occurrence of Charybdea at the surface of quite -shallow water and near the shore (which is quite at variance with former -observations, that the Cubomedusæ are essentially deep-sea forms) are -further borne out by his observations at Port Antonio. As already noted -in the Introduction, Charybdea was here found in abundance in quite -shallow water and near shore, but on the bottom instead of at the -surface as at Port Henderson. It is possible that the animals had been -active near the surface earlier in the morning and that some unknown -conditions determined their settling to the bottom earlier in the former -place than in the latter. - -Conant’s conjecture, “whether these were their natural conditions, -or whether the two forms,” Charybdea and Tripedalia, “were driven by -some chance from the deep ocean into the harbor and there found their -surroundings secondarily congenial, so to speak,” seems to be borne out -in favor of the former supposition (for Charybdea at least),--that these -are their natural conditions and that Charybdea Xaymacana is essentially -a shore form. - - -AURELIA AND POLYCLONIA (CASSIOPŒA) - -Experiments 42-53. - -Many of the observations on these forms relate to the rate of pulsation. -In an Aurelia, following the removal of a lithocyst, there was a pause -followed by pulsations. In about two minutes rhythmic pulsations were -renewed. Four minutes after the operation there were nineteen pulsations -to the half minute, while twenty minutes after there were only nine, -and these in groups of six and three. The normal rate of pulsation was -twenty-five to the half minute. - -Polyclonia behaved much in the same manner as Aurelia. Upon the removal -of lithocyst pulsations continued, but in groups with short pauses. The -normal rate of pulsation was twenty-seven to the half minute, while three -minutes after the operation it was seventeen, and eleven minutes after, -fifteen to the half minute. The tissue connected with a removed lithocyst -gave contractions. Placing a Polyclonia in fresh sea-water more than -doubled the rate of pulsation, which, however, soon fell to the normal -rate, and lower in one instance. In small individuals the rhythm is -decidedly more rapid than in those of larger size. The few observations -on this point would seem to show that it is in inverse proportion to the -squares of the diameters of the bells. - -The removal of a single oral arm or of the whole eight, in Polyclonia, -had much the same effect as the removal of a lithocyst: there was a -decided slowing of the rate of pulsation, while the immediate effect of -cutting was an acceleration or a return to near the normal rate. About -a day later this same animal had quite regained its normal rate of -pulsation and continued to live over two weeks. A long latent period -followed the cutting of an arm, before the stimulation of cutting -manifested itself. - -An Aurelia, with all its lithocysts removed, still gave spontaneous -and coördinated contractions after allowing time for recovery from the -operation. This was the result in one instance, while in several others -only a few contractions were observed. Removal of the sixteen marginal -bodies (lithocysts) in a Cassiopœa produced paralysis for a time but -recovery soon followed. A Polyclonia with its entire margin removed was -paralyzed but had so far recovered in a day as to be able, at intervals, -to give spontaneous pulsations. - -The removed margin of a Polyclonia pulsated vigorously. This margin was -then split so as to make a ring within a ring but connected at one point -by a small bridge of tissue. The waves of contraction, which always -originated on the ring with the lithocysts, passed the bridge to the -inner ring quite as Romanes experienced. The outer ring was next split -so as to separate the exumbral portion from the subumbral, when it was -found that the contractions always originated from the latter. Seven -days after its removal, this same margin was still alive and pulsating -vigorously, and broken-off pieces of the subumbral portion were pulsating -by themselves. Fifteen of the ganglia were removed. It was then found -that while most of the pulsations originated at the remaining ganglion, -now and then contractions originated in other parts where no ganglion -remained. Two days later this margin was still alive with contractions -originating as often from other parts as from the ganglion. A similar -observation was made on a margin of Cassiopœa. - -A Polyclonia with the eight lithocysts of one side removed, to compare -with a normal one, gave no evidence of affected coördination. - -An oral lobe from an Aurelia could give contractions some minutes after -removal. - -In another Aurelia a circular cut was made about the base of the oral -lobes through the epithelium of the subumbrella. The animal could pulsate -well enough but coördination seemed a little affected, while in another -one with a like cut but semicircular, no effect was noticed. - -These results on the removal of the lithocysts (and margin in Polyclonia) -in Aurelia, Polyclonia and Cassiopœa agree quite with those on Charybdea -and, of course, also with Romanes’ and Eimer’s results as to paralysis -and recovery following the removal of the lithocysts, or margin, in -Aurelia, Cyanea, etc. I recall no similar observations, however, on -removing a single lithocyst, and the question of an explanation for -the slowing of the rhythm thus brought about arises. Romanes gives as -an explanation for the slowing of the rhythm (Aurelia, Cyanea, etc.) -following the temporary acceleration upon removing the manubrium or a -portion from the center of the bell, as due to a lack of an afferent -stimulating influence upon the ganglia from the excised tissue. May -a similar explanation not serve to explain the slowing following the -removal of a single lithocyst, above noted? The removed lithocyst could -no longer give its efferent stimulus to the remaining ganglia nor to the -tissue, so that the former would have a weaker stimulating influence, -in consequence of which the latter (the contractile tissue) would be -deprived of a part of the original stimulus of the remaining ganglia as -also of that of the removed ganglion. The whole would thus result in -giving to the contractile tissue a weaker stimulus, which, again, would -require longer and greater recovery on the part of the tissue in order -to be set off by the stimulus at hand. This explanation is given on the -basis of Romanes’ theory of rhythmic contraction previously explained. - -Of course, it may be suggested that the musculature had lost tonus, -due to the lack of influence of the removed ganglion (lithocyst), in -consequence of which there was a lowering of irritability on the part -of the contractile tissue. This would require a greater summation of -stimulating influence (Ganglionic theory of contraction) on the part of -the remaining ganglia to set it off. Again, the loss of irritability -on the part of the contractile tissue may have been due to a lack of -nutritive influence from the removed ganglion. - -Romanes’ explanation, that the slowing of the rhythm following the -removal of the manubrium and central parts of the bell in Aurelia and -Cyanea is due to a lack of an afferent stimulus on the ganglia from the -removed tissue, likewise explains the similar results obtained by Conant -by removing the oral arms from Polyclonia. - -The fact that a margin of Cassiopœa and also of Polyclonia, connected -with but one ganglion, often originated contractions in other parts as -well as from the ganglion, seems to show that motor centers resided -in the margin outside of the ganglia. This would be somewhat at -variance with Romanes’ conclusion, that no such centers existed in the -Scyphomedusæ. Conant does not state whether the Polyclonia margin in -question was kept in fresh sea-water or whether the water was not changed -during the seven days. If the latter is the case, then some poisonous -compounds may have been formed that acted as a stimulus much as weakly -acidulated water served Romanes in producing rhythmic contractions in -deganglionated bells. - -Again, while it is true that no ganglia are known to exist in the margins -of the Scyphomedusæ outside of the ganglia in the marginal bodies, yet, -ganglion cells and nerve fibers are found in the subumbral part of the -margin as well as in the rest of the umbrella. And as I know no reason -why scattered ganglion cells may not function as ganglia, it is possible -that the contractions in question were spontaneous. - -Finally, is it possible that the remaining ganglion originated the -contractions in different parts of the margin, thus acting at a distance -from the points at which contractions originated? Romanes gives an -instance in which he believed to have evidence that this was the case. -Upon a final consideration I am inclined to this latter explanation. - - -SUMMARY. - -Summing up for Charybdea, we have seen that it is very sensitive to -light, strong light as also darkness inhibiting pulsations, while -moderate light stimulates it to activity. Also, a sudden change from -weaker to stronger light, or _vice versa_, may inhibit or stimulate to -activity respectively. This behavior of Charybdea seems to be correlated -with its habit of life on the bottom. We have no reason to doubt but that -the eyes of the sensory clubs are the seat of light sensation. - -The experiments on equilibration are negative, giving us no certain -light on the function of the concretions, though it appears that they -may serve, in part at least, for keeping the sensory clubs properly -suspended. Their function in giving the animal sensations of space -relations is not, however, excluded. - -Excision of the sensory clubs demonstrates that they are the seat of -important ganglionic centers, the removal of which results in temporary -paralysis and weakness. That they also are the seat of organs (eyes, -network-cells, concretions) that are of importance in giving information -in the life of Charybdea, is evident from the reaching motion of the -proboscis after the removal of the sensory clubs. Other centers of -spontaneity in their order of importance probably are: the radial ganglia -(one experiment); the interradial ganglia (?); the suspensoria, as shown -by their supplying stimuli to isolated pieces of the sides connected with -them; the frenula and the velarium, the latter of which gave contractions -when removed with the frenula or in pieces only. No evidence is given -that the frenula or the velarium can impart their contractions to other -tissue, though this seems probable for the former. The proboscis can also -contract of itself. - -Reflexes between the velarium, frenula, subumbrella, sensory clubs, -nerve, and any one pedalium, on the one hand, and the pedalia on the -other hand, are very common, and point to the pedalia with the tentacles -as organs of defense and offense. The pedalia serve also as rudders in -swimming. - -Finally, as judged by the results in this paper, Charybdea seems to -occupy, physiologically, a position intermediate between the Hydromedusæ -and the Scyphomedusæ. In its great activity as a swimmer, in its response -to light, and in its reflexes it is Hydromedusan, while in the paralysis -and recovery following the removal of its marginal bodies, as also in its -response with several pulsations instead of one, when a deganglionated -bell is stimulated, it is Scyphomedusan. - -The observations on the Discomedusæ, Aurelia, Polyclonia, Cassiopœa, -demonstrate the existence of motor nerve centers in the marginal bodies; -but that other centers are present is shown by the recovery of pulsation -following the removal of the marginal bodies or the margin. These results -are mainly confirmatory of those of Romanes and Eimer. They differ from -these in the fact that margins of Polyclonia and Cassiopœa, with only one -ganglion attached, originated contractions distant from the ganglion. -Removing of a single lithocyst resulted in a slowing of pulsation, as did -also the removal of the oral lobes, though the immediate effect in the -latter case was an acceleration. Isolated pieces of the subumbrella could -contract. - - - - -DR. CONANT’S NOTES. - - -Below follow Dr. Conant’s notes. They are printed about as Conant left -them. Their order of succession, however, has been changed to bring -similar experiments together, while useless and often repeated ones -have been omitted, and short elliptical sentences completed. Where the -present writer wished to add any explanation, the same has been placed in -brackets. - - -CHARYBDEA. - - -_Light and Darkness._--1. Eight medusæ, in a deep glass jar and covered -by a black coat, except one inch around the top, were placed in the -dark-room. - -a. When light from a lamp was thrown on the surface (one inch) layer, the -animals were active near the surface; when the light was withdrawn, one -or two were on the bottom and not moving but were probably pulsating. - -b. After four or five minutes in the dark, three or four besides a feeble -one are on the bottom. It took about two minutes to get them all to -swim [by the lamp]. Of the three on the bottom, one, at any rate, was -not pulsating. [Three other attempts like a and b were made, with very -similar results.] - -2. Experiment No. 1 was repeated several weeks later. Four in a large -round glass dish were placed in the dark-room. A lamp being held to the -dish all but one were found to be on the bottom. That one quickly went to -the bottom, while two of those on the bottom quickly came to the top. In -two or three minutes the one that had gone to the bottom began to pulsate -and at about the same time the other one that had remained on the bottom -also began to pulsate, while the two that had gone to the top stayed -there swimming very actively. [Repeated with like results.] - -3. Fresh ones did not show the reaction to light after darkness so -well as did those in the experiments previously recorded. They were -experimented with about nine A. M., while usually they were tried later -in the day. I had rather suspected from previous work that they would not -react so well when fresh. - -4. a. In walking with the jar (1) of jelly-fish of experiment 1 from -the dark-room to the back porch of the laboratory (fifty steps), in the -bright sun and a cool breeze, all were found upon entering the laboratory -door to have settled to the bottom and most of them to have ceased active -swimming. In five minutes two or three were swimming somewhat, and in -five minutes more all but one or two (eight in all) were swimming. - -Walking with the jar about the laboratory did not suffice to make any -change in their swimming, nor did blowing on the surface make any -appreciable change. - -b. Upon taking the jar to the back porch and placing it on the stone or -cement flags, in the shade and a cool breeze, in four minutes time all -were on the bottom not even pulsating. - -Upon replacing them on the laboratory table all began to swim about at -once. [Repeated.] - -c. The jar (1) was placed on the back porch again; in fifteen seconds -three were on the bottom; in one-half minute all but one. In three or -four minutes all were on the bottom, but two were swimming lively and the -others pulsating. In another minute all were swimming. - -d. The jar (1) was tried again, not resting it on the flags but holding -it by my hands on the sides. The effect was just as quick; they stopped -pulsating at once. By the time I had got back to my table in the -laboratory, one was at the surface and another arrived just as the jar -was set down. - -[Several other experiments of an order similar to those just noted were -tried, with very similar results.] - -5. Two buckets stood side by side in the laboratory. One bucket (1) had -more Charybdeas in it than the other bucket (2), and also had more since -brought in (about an hour). The water of one (1) was also more discolored -and with more organic matter (sea weed, etc.). In the laboratory the -animals were active on the surface of both buckets. Placed in the -sunlight on the porch, no breeze, the sun slanting so that one side of -the water in the buckets was bright while the other side was shaded, the -jelly-fish in (1) went mostly to the bottom, while those in (2) seemed -unaffected though some showed a tendency to go to the bottom after a -longer exposure. The experiment with (1) was repeated and it took some -five minutes for them all to go to the bottom. In a few minutes after -replacing them in the laboratory several were active again on the surface. - -6. Jar (a) with five large ones stood on my table; they were quite -active. Placed in the sun (no breeze), on the porch, one or two sank -to the bottom at once and the others seemed to slow their activities -somewhat but not very markedly. In a few minutes all were swimming, -apparently more actively than before, in the bright sunlight. - -[In other experiments Conant shows that it is not the stimulus of walking -that causes them to swim when carried into the room, for they would not -swim when he walked with them on the porch. Also, he shows how they may -change, some swimming, others not, when left for some time in any one -place.] - -7. In a tumbler were two pulsating very vigorously. Placed in the bright -sunlight, very little breeze now and then, they showed no change whatever. - -8. Some in a jar were covered with a black coat. The coat was taken off, -and almost immediately they stopped pulsating, or pulsated but feebly, -and sank to the bottom. The coat was put on again with one part near the -bottom of the jar exposed. Almost at once, the animals, which were quite -motionless, pulsating but little, resumed pulsation, which became more -and more vigorous, and quickly swam to the top again. It seems plainly -to be a reaction to light. [Such experiments as this were repeated at -different times with very like results.] - -9. A bucket with several bobbing actively on the surface was set out in a -smart shower, and the animals continued bobbing on the surface as before. -I could not see that they made the slightest attempt to go below. - -There can be no doubt but that there is an individual difference in -sensitiveness to the reaction of light after darkness. E. g., I just -removed the coat from a dish with four in it; one went to the bottom at -once, another presently, a third remained active at the surface, the -fourth when noticed was on the bottom. - -There is also a difference in the length of time they stay on the bottom -as well as in the quickness in the response to light. Some recover very -quickly, should say in less than a minute, and at once become very -active. Some stay for a long time and only resume activity upon the coat -being placed over them. Perhaps this explains some of the observations in -Experiment 1. - - -_Sensory Clubs._--10. All four concretions were removed and the animal -stood the operation well. It swam more restlessly, however, than others -did in the same surroundings. It seemed at first to show a trace of loss -of sense-perception. It swam up, and down again, more changeable than -those intact, which stay rather more constantly either on the bottom -or at the surface. This may, however, have been due solely to the -restlessness of the animal after the operation. Later it swam actively -for by far the most part on the surface only, which points to the truth -of the preceding statement. - -It showed no reaction to _light_. A coat placed over the jar was removed, -when it was found to be on the surface and it remained there. This was -twice repeated. I noticed specially that on pushing the bell above the -surface of the water it at once turned and went deeper as the normal -animal does. Finally, given another a trial with removing the coat from -the jar, it went to the bottom as the normal animal usually does. After -this, when next seen, it was keeping to the bottom. [This experiment was -repeated on another occasion with almost identical results, no loss of -sense-perception being noticeable.] - -Sometimes it seemed as if access of _light_ at removing the coat acted -as a stimulus to one or more of those that were quiescent on the bottom. -This was noticed again on the following day. - -11. Two more were operated upon. These did not stand the operation well -and stayed on the bottom, one swimming, while eight hours later one -was in better condition (pulsating) than two left in the same dish for -comparison. - -12. a. Three clubs were cut off leaving only the stalks. A temporary -paralysis of the power to swim was the immediate effect. Later it -partially recovered this power. The proboscis, which was previously -quiet, now showed convulsive twitchings and movements. It continued for -some time to move to one side and then the other (after short pauses of -varied length) as if to grasp some object. The lips of the _proboscis_ -were also moving and at times expanding. Often the movements were towards -the side on which the club was uninjured. - -b. The fourth club was next removed. A temporary paralysis as before -resulted, followed by a quick recovery of pulsation; but the animal was -now much weakened. The movement of the proboscis continued--shortening, -lips expanding, moving to this side or that. The pulsations of the bell -were kept up even when too weak to swim. - -c. The sensory niches of this same animal were treated with 2.5 per cent. -acetic acid by means of a pipette. The stalks of all four clubs showed -white. Pulsations ceased. The velarium showed feeble local contractions. -The movements of the proboscis and suspensoria drawing down the stomach -continued. Upon stirring the animal it gave rather feeble, somewhat -convulsive pulsations with local (fibrillar) contractions; the pulsations -in some cases were pretty well coördinated, but were more on the -twitching kind. - -13. Three clubs were removed. The animal pulsated well, only a little -less strongly, perhaps. After a minute or two the fourth club was -removed. It pulsated almost immediately, perhaps thirty seconds after the -operation. It swam very well and pulsated feebly five hours after the -operation. - -14. One from jar (a) (Experiment 6) was operated upon. When the first -club was cut off there was a paralysis of pulsation followed by a quick -recovery. Cutting off the second club seemed to stimulate pulsation, -the third to diminish it; after cutting off the fourth club it still -pulsated. When placed in a large jar it pulsated on the bottom, but not -strong enough to swim. The pulsations were fairly regular and sometimes -seemed to occur in groups of two, but these groups were not well marked. - -15. Another one from jar (a) was taken. One club was cut out, upon -which there was a very temporary paralysis followed by good pulsations -afterwards. The _proboscis_, as in all cases noticed, gave active -movements to this side and that side. These movements of the proboscis -were often very quick and definitely directed as if a well defined -stimulus were given. After the operation one _pedalium_ contracted so as -to be at a right angle to the main axis of the bell; shortly a second -pedalium also contracted. Placed in a small round dish the animal swam -actively. - -A second club was removed, and it swam as well as before. After fifteen -minutes it was not swimming but pulsating against the jar. Upon stirring -it a little it swam vigorously ten to fifteen strokes and then stopped. -It seemed weak and its movements appeared not so definite, though this -might be due to weakness. - -A third club was removed. The only change seemed to be rather greater -weakness. - -After about five minutes the fourth club was removed. Paralysis of -pulsation followed. It had the power to contract its _pedalia_ when these -were rather vigorously stimulated with a needle. It also gave one feeble -pulsation when so stimulated. - -16. The sensory clubs were removed from another. After removal of -the third one it still pulsated actively, but stopped completely and -apparently for good after the removal of the fourth club. Another one -stopped pulsating apparently for good upon removing the third club. - -17. All four sensory clubs were removed from one, cutting as high up as -possible so as to remove the endodermal tract of nerve fibers of the -peduncle. It pulsated afterwards apparently the same as if the stalks had -been left intact. - -18. A small piece surrounding a sensory club and including the _margin_ -can contract by itself. The piece observed pulsated with quick pulsations -and rhythmically but intermittently. After a fresh cutting away of such -a piece, the portion of the _velarium_ attached was seen to contract -rhythmically, while the rest of the _subumbrella_ was not so seen. The -part of the subumbrella above the radial ganglion that was cut off did -not contract by itself. The same portion of the velarium cut off did give -contractions. - -19. A sensory club with the surrounding region cut out pulsated -rhythmically; when the club was cut from the end of its stalk pulsation -stopped. This observation was repeated on another, and contractions were -seen after the removal of the club. A piece of the _subumbrella_ wall -from the same animal gave contractions now and then even after an hour. - -20. The normal position of a sensory club seems to be with the concretion -almost at the lowermost end; often with it certainly lowermost, but -probably oftener with the perpendicular passing through the center of the -attachment of the club to its peduncle and just by the inner edge of the -concretion. The eyes point inwards. - -When the animal is on its side the concretions are always quite -lowermost. When the animal was inverted the tendency was for the -concretions to be lowermost. In this position the eyes may point in -several directions. In one instance those of one club pointed rather -outwards, while of two other clubs they pointed more in the plane of the -body wall. (See also Experiments 24, 29.) - - -_Nerve._--21. Cutting the nerve eight times, once on each side of each -sensory club, produced no loss of coördination in pulsating. The animal -was weakened, however, by the operation, which was made drastic to insure -cutting the nerve; but it was still able to swim. This experiment was -repeated four times. - -22. That coördination was continued after the nerve was cut was -proved beyond doubt by cutting from the edge up (eight times) so as -to perfectly separate the sensory clubs and the pedalia. Pulsations -continued synchronously in all four sides--not the slightest evidence -that one side contracted out of time with the others. - -23. The eight cuts were made as in the preceding experiment with no loss -of coördination noted. When the cuts were carried up to the base of the -stomach, however, coördination ceased. The four side pieces seemed to -contract each in its own time. Only two sides could be observed at one -time, and they at any rate did not contract synchronously. One side often -gave two contractions while the other side rested or gave one. - -Yet, a little later, three of the sides at any rate showed a pretty -good coördination. The fourth was smaller and did not seem to get into -the game much--it went more on its own schedule. The four pieces were -then cut apart and placed together under a dissecting microscope. No -coördination at all could be made out. No evidence, therefore, of any -definite rate of pulsation inherent in the sensory clubs. - -Cutting the nerve causes the _pedalia_ to forcibly contract inwards. - - -_Side, Subumbrella._--24. A whole side was cut out, the transverse -cut being above the sensory organ so as to take off [leave off] the -radial ganglion also. This pulsated, or rather contracted, nicely. The -upper end had been cut just through the _suspensorium_. It especially -gave twitchings like the twitchings of the stomach. The piece was then -halved transversely, when the upper part containing the portion of the -suspensorium twitched as before while the lower part was not seen to -contract again. This was repeated with the same result, except that a -portion of the lower part gave a slight contraction several times. The -part that contracted was at the upper end of the piece, _i. e._, nearest -the _suspensorium_. The contractions were also more longitudinal than -transverse, as the regular contractions would be. - -The piece connected with the sensory clubs of course pulsated nicely. -Upon cutting off the sensory club from the stalk, pulsation ceased, but -twitching of the _velarium_ continued. This was repeated with the same -effect. - -In the same animal, in cutting off the sides, the stomach was left, the -cut being through the gastric ostium. The floor of the _stomach_ was now -cut off by cutting out the four interradial points of attachment. The -stomach and the proboscis gave vigorous contractions and tied themselves -all up so that I could not cut off the proboscis. - -The four pieces of the floor of the stomach left on the interradii gave -contractions nicely. The phacelli continued their squirming movements. - -25. Cutting off the whole aboral end of the animal excites to very rapid -pulsations of the remaining part. The stream, as shown by particles -in the water, is apparently stronger out the aboral end than past the -velarium. - -It seems that I get no good evidence that the subumbrella is able to -contract of itself without connection with special nerve centers. In the -one case noted (Experiment 31) I could not be sure but that the part that -contracted was intimately associated with the suspensorium or frenulum. - -26. A piece of the subumbrella cut off and having, so far as I could -determine, no connection with ganglia, frenula, or suspensoria, gave -contractions. Another piece was not seen to contract. - -A small piece of the subumbrella connected with a club can contract. The -proboscis can give contractions of itself when cut off with the base of -the stomach. Even a cut-off lip can twitch by itself. A portion of the -subumbrella by itself also showed twitchings. (See also Experiments 18, -19, 25, 26, 29, 47, 49.) - - -_Pedalia, Velarium, Radial and Interradial Ganglia._--27. The pedalia -with their tentacles were cut off at their bases to insure cutting out -the interradial ganglia. The animal could pulsate well enough, but -intermittently and without much progress (the velarium, of course, being -injured). Cutting one pedalium caused the others to contract. - -28. When the pedalia were cut off from one, the power of direct motion -was entirely gone. It swam in circles, turned summersaults, changed its -course continually, the oral end getting ahead of the aboral end, or -trying to do so. The whole power of balancing was gone. It seemed excited -by the operation and swam continually. [Repeated.] - -29. The pedalia can be made to contract inwards by stroking their outer -edge with a needle. This was noted last year and has been seen several -times this year. Their inner edge is not so sensitive. - -Touching a _sensory club_ caused the pedalia to contract inwards in two -cases. - -The pedalia could be made to contract by giving the subumbrella a -prick,--generally a rather severe one was necessary. The upper part -of the subumbrella seems not so sensitive as the lower part and the -proboscis, and the base of the stomach did not give any reflex at all -(two specimens). One of the two could be made to give the reflex only -with much difficulty. This was a very lively one. It would even stand -severe pricks on the nerve, or even through the region of the sensory -clubs, without contracting the pedalia or stopping pulsations. - -Cutting the frenula seemed not to affect the ability to swim well. -Cutting in this region brings about the reflex of the pedalia. - -In the preceding fish the _velarium_ was cut away wholly in some places, -in other places it was left only as ragged strips. The pedalia became -very strongly contracted and the _tentacles_ were brought inside the -bell. Pulsations that seemed strong produced much less progress than with -the velarium intact. [Repeated.] - -30. One with the whole _margin_ cut off still gave pulsations. Upon the -removal of the region of the _radial ganglia_, however, pulsations were -seen no more. - -The _velarium_ in the above continued to give twitchings. The four -pedalia were cut off with plenty of the tissue at their bases to insure -the removal of _interradial ganglia_, and twitchings of the velarium -with irregular contractions continued. No full contraction all around -the velarium was noticed. When all the tissue was trimmed off as nearly -as possible down to the _velarium_, the latter still gave twitchings and -irregular contractions as before,--even more so as if excited by the -operation. The power of originating contractions evidently resides in the -velarium or in the ganglion cells of the frenula just as it does in the -proboscis and the floor of the stomach. - -Small pieces cut from between the pedalium corners and the frenula, so as -to have tissue on them from neither, could contract by themselves. (See -also for Pedalia, Experiments 15, 23, 41b; Velarium 18, 41c.) - - -_Tentacles._--31. A cut-off tentacle can contract by itself, sometimes -with squirming contractions. A prick at either end can produce a forcible -contraction. A slight prick at the distal end may produce a local -contraction. The proximal end is more sensitive, but this difference -is not very marked. One with only the tentacles removed seemed to be a -little less able to guide itself well. - - -_Proboscis, Stomach, Phacelli._--32. The lips of the proboscis are -highly contractile by themselves. The movement of the stomach and the -phacelli goes on, after the lips are cut off, with increased vigor, due -to the stimulus of shock. The vigor and frequency of their contractions, -however, diminish quicker than that of the cut-off lips. (See for -Proboscis, 12, 15, 18, 26, 29; Stomach, 18, 24, 29, 31; Phacelli, 18, 24, -31.) - - -_Temperature._--33. Temperature does not seem to have much effect. Some -placed in a tumbler half full of water, in the bright sunlight, swam -vigorously over three-fourths of an hour. The water was quite warm to the -hand. - -34. The above experiment was repeated with the same results. A -thermometer placed in the water with them showed 92° F.; hung in the sun -near by, it showed 94° F. - -Ice in the water did not stop their pulsating temporarily or permanently, -except that it did for a short time after being held against one. Even -then it took some time (fifteen to twenty pulsations) before it produced -any effect. - -35. Ice placed in the water again showed no marked effect. They swam as -lively as ever. Some, after pulsating against the ice for a little while, -seemed to be less vigorous, but quickly recovered in another part of the -jar. Others did not seem to be the least bit affected by contact with the -ice. - - -_Food and Feeding._--36. I tried to feed one. A red and a white copepod -were put into the subumbrella cavity. No attempt to eat it was observed -in either case, though the copepods remained in the subumbrella cavity -for some time. - -Animals found in the stomach of Charybdea: small fish were most -frequently seen; at another time a small stomatopod; again, a small -polychæte; small shrimps; amphipod. - -Those taken on August 16th (3 to 4 P. M.) seemed to have, for the most -part, food in the stomach, and this more so than those taken in the -morning. - - -_Occurrence of Charybdea._--37. In the first tow on the bottom (with a -net made of mosquito-netting and weighted with rocks in order to sink it) -the haul was forty. I do not think that we could have been towing more -than four or five minutes. The time was about seven A. M. A light breeze -was blowing and there had been a heavy shower a half-hour previous. - -38. The usual time of towing was about 6.30 to 7.30 A. M. The water was -four to five feet (1.2 to 1.5 m.) nearest shore but deeper farther out. -At this time of day one could count on getting plenty of the larger sized -(15 to 20 mm.), many small ones, but very few of the smallest. This was -the experience of several mornings. - -On August 12th I towed about nine A. M., and got but few of the larger -sized, many small ones, and very many of the smallest. - -The next day (7.00 to 7.45 A. M.) those obtained were mostly of the -larger size. On the same day (3 P. M.) others of the party towed at the -same place and obtained but few. - -On another day I towed in the afternoon (3 to 4 P. M.) and obtained great -numbers as I usually did in the morning. - -39. We towed about 7.30 to 8.30 at night. Very few Charybdeæ were taken. -On this evening we towed five times in the same locality, and obtained -but seven or eight specimens. Towing with the same net on our way home, -it was filled with Aureliæ and five or six Charybdeæ. It seems as if -Charybdea came to the surface at night. Those towed in the evening were -dead the next morning. - -The next morning Richard, our colored attendant, towed from 5.30 to 6.30. -There were heavy showers. The usual find of large and medium ones was -obtained. There were only two with planulae. - -40. The material of September 2nd was obtained about six A. M. They were -mostly of large size. In all only fifteen or twenty were taken. Richard -explained the small number by saying that the bottom had changed in the -locality where we usually towed and that he got no weeds in his net, but -mud. - -The next day more were brought in by Richard (6.30 A. M.) There were -rather more than yesterday but the quality was the same. There were three -with planulae. - -On another morning Richard brought in a great many, about a hundred. -Among these there were three with planulae (light-colored and budding); -on a previous day there was one with the reddish-brown kind and with a -mouth. - - -_Activity of Charybdea._--41. a. About five o’clock in the morning -a Charybdea was taken in the tow. It was in good condition swimming -incessantly round and round without change of direction, in a jar of -about twenty centimeters in diameter. It came to the surface every now -and then, after eight to fifteen pulsations. The tentacles and the -phacelli were of a lilac shade. If a pencil was placed in its way it -would pulsate against it repeatedly without any effort to dodge around it. - - 6.58 A. M., 124 pulsations were counted to the minute. - 8.00 “ 124 “ “ “ “ “ - 9.25 “ 136 “ “ “ “ “ - 10.15 “ 131 “ “ “ “ “ - 11.00 “ 146 “ “ “ “ “ - -At 10.15 it went around the dish in eight seconds, taking eighteen or -nineteen pulsations. If a bright platinum spatula or a black pencil was -placed in its circuit it would repeatedly butt against it each time it -came around. After the second or third pulsation against it, however, it -seemed to have some sense to change its direction. - -b. The _pedalia_ have no perceptible action of their own. They move -inwards slightly toward the axis at each pulsation, but scarcely as much -as one would suppose from their attachment to the pulsating margin. It -seems as if they were for “winging” the moving animal more than for -anything else. - -c. The _velarium_ is loose and it flaps. It seems to take part in -swimming something more than the passive diaphragm function,--i. e., it -straightens out during the recovery after each contraction of the bell. - - -AURELIA AND POLYCLONIA. - -[The following experiments were performed at Port Henderson, Jamaica, in -1896.] - -42. May 12th. An _Aurelia_ was pulsating normally at the rate of -twenty-five or twenty-six pulsations to the half-minute. One lithocyst -was cut out, when a few contractions, evidently caused by the stimulus -of cutting, followed; then, rest. In the first minute there were only -about five pulsations. In two or three minutes rhythmic pulsations were -resumed. Four minutes after the cutting there were nineteen pulsations -to the half-minute. About twenty minutes after there were nine to the -half-minute, in groups of six and three. - -A _Polyclonia_, about four and one-half inches (115 mm.) in diameter, -gave twenty-six or twenty-seven regular pulsations to the half-minute. -After one otocyst was removed, pulsations continued, but in groups with -intervals of pause: _e. g._, thirteen, pause; ten, pause; six. Three -minutes after the removal of the lithocyst there were 5, 3, 1, 3, 5, -or seventeen pulsations to the half-minute. Eleven minutes after the -operation there were fifteen to the half-minute. The removed lithocyst -and surrounding tissue gave contractions. - -43. May 13th. The _Aurelia_ was in rather poor condition but would -pulsate upon being stirred. The other seven lithocysts were removed when -only a few contractions originated thereafter. - -The _Polyclonia_ was in good condition, but was pulsating only -intermittently when first seen in the morning. When the remaining seven -lithocysts were cut out and no more pulsations were observed, the oral -arms could still move. - -May 14th. Both were found dead upon returning in the evening. - -44. May 15th. An Aurelia and a Polyclonia were taken in the morning. The -_Aurelia_ was two and one-half to three inches (62.5-75 mm.) in diameter, -with three tufts of phacelli, three oral arms and seven lithocysts. -The _Polyclonia_ was normal and seven or eight inches (175-200 mm.) in -diameter. - -In the _Aurelia_ all the lithocysts were removed. Spontaneous and -coördinated contractions could still occur after time had been allowed -for the shock from the operation to pass away. The next day the animal -was still alive and pulsating, but ragged, and the next day following was -quite dead. - -In the _Polyclonia_ the normal rhythm was fourteen pulsations to the -minute. Some pulsations were apparently quicker than others and the -intervals were not the same. Thirteen, ten, and twelve pulsations were -also counted. After putting the animal into fresh sea-water, it pulsated -thirty-three to the minute. Six minutes later it was still pulsating -at the same rate, while in four minutes more eleven pulsations, many -of which were in groups of two, were noted. In five minutes more it -pulsated eleven times to the minute with only one double pulsation. One -_oral arm_ was then cut off and the rhythm counted about one minute -afterward--fourteen pulsations, then a pause of fifteen seconds, then two -pulsations, in all sixteen to the minute were counted. About ten minutes -later there were eight pulsations, two or three minutes later only three, -while in two or three minutes more only three. There was a long latent -period--two or three seconds--before the stimulation of cutting off the -arm made itself evident in the rhythm. - -A second oral lobe was removed. Then there followed twenty-four -pulsations, a pause of two seconds, and two pulsations, in all twenty-six -pulsations to a minute. The rate of pulsation soon fell to the previously -abnormal low rate. - -Third lobe removed: 21 pulsations in first half minute and then 16, or 37 -per minute. - -Fourth lobe removed: 17 pulsations in first half-minute plus 13 gives 30 -for the minute. - -No difference in the coördination of the animal was shown as a result of -the removal of one-half the number of oral arms. - -Fifth lobe removed: 17 pulsations plus 15 equals 32 to the minute. - -Sixth lobe removed: 17 in first half-minute plus 4 in the second -half-minute gives 21 pulsations for the minute. - -Seventh lobe removed: 17 plus 9, or 26 per minute. - -In all these instances the rhythm in the second half of the first minute -was irregular and intermittent. - -Seventeen and then seven pulsations were provoked after the animal had -become quiescent, or nearly so, by merely handling it. - -45. Eighth oral lobe was removed and pulsations stopped. The next day -the animal was in good condition. The pulsations counted in the evening -were 12, 14, 14, 11, per minute. The rhythm was not regular; there was a -tendency to groups of twos, threes, or more, but no prolonged intervals -of rest were observed. When placed into fresh sea-water, the pulsations -were fourteen to the half-minute or twenty-six to the minute; seventeen -to the half-minute, and thirty-three to the minute were also counted. -This specimen gave spontaneous contractions during two weeks, after which -it was thrown out, the aboral end being eaten through and little or no -regeneration having taken place. - -46. Two more were operated upon: A. Its rhythm was 18, 14, 17. Its entire -margin was cut off. The separate pieces of the margin pulsated, 6, 7, -4, 6, 7, 9. The animal seemed paralyzed by the operation; it responded -by a contraction now and then to stimulation but gave no spontaneous -pulsations. B. Its rhythm was 17, 15, 12, 12. All its _oral arms_ were -removed. Its rhythm was only raised to seventeen and not perfect. In -twenty-five minutes it had fallen to eleven, in four hours to ten -pulsations [per minute]. - -May 22nd. A and B are living as also the pieces of the _margin_ of A; -all are giving spontaneous pulsations now and then at comparatively long -intervals--even A, with its margin removed. - -May 26th. Everything is still living. The one with the margin cut (A) -counted sixteen and nineteen pulsations per minute, though this was not -kept up all the time. - -June 2nd. A and B and pieces are still living and contracting -spontaneously. It is now two weeks, and they were thrown out eaten -through at the aboral end with little or no regeneration. - -47. The margin was cut off another one (C) and it was then paralyzed. The -margin contracted vigorously by itself. The margin was next split, but a -connection of about one-half an inch wide was left between the two rings. -Over this bridge the contractions passed from the outer and inner ring. -The inner ring did not originate any contractions. Both rings were then -cut near their connecting bridge of tissue and the larger ring with the -marginal bodies was split longitudinally so as to separate the exumbral -from the subumbral portion. It was found that the contractions started -only from the subumbral portion while the exumbral portion did not -contract at all. - -June 5th. Five of the eight small pieces of C were not seen to contract -either to-day or yesterday. A slow rotary motion was observed in -some of the pieces suggesting ciliation, but no cilia or currents -pointing to ciliation were seen with a low power. C was seen to pulsate -spontaneously. Possibly it did yesterday but it was not watched closely. -A piece of the subumbral surface of C broken off (not from the margin) -was found to contract spontaneously. - -48. June 6th. In a fresh one (D) from Port Royal, the eight lithocysts of -one side were removed in order to compare its movements with an intact -one. Coördination was apparently unaffected. - -June 9th. The margin of C is still pulsating vigorously. Parts of the -subumbrella broken loose from the strip pulsated by themselves now and -then. Fifteen lithocysts were removed, leaving only one at the end of the -strip. It was found that with this single ganglion (lithocyst) left, and -originating most of the contractions, now and then a contraction would -originate at another part of the strip where there was no ganglion. Three -days later contractions originated as often from other parts as from the -ganglion. - - -CASSIOPŒA. - -[The remaining experiments were all performed in 1897, at Port Antonio.] - -49. Removal of the sixteen marginal bodies caused paralysis for a time; -then recovery followed. - -Contraction was limited to the subumbrella. - -A portion of the _subumbrella_ not from the margin can contract by itself -as well as a portion of the margin with the marginal bodies (lithocysts). - -In the _margin_ cut off as a strip with only one marginal body attached -at one end, contractions sometimes started from the opposite end. - - -AURELIA. - -50. Size, seventeen or eighteen millimeters. Pulsations, thirty-two. -Lithocysts, nine. The operation consisted in the removal of the -concretions with as little injury to the pigmented parts of the marginal -bodies as possible. One whole marginal body, however, was removed in the -operation. Soon after the operation the pulsations were 28, 26, 20, 20, -per minute. - -Another one; size fifteen millimeters. Pulsations were forty per minute. -The operation consisted in the removal of the concretions and pigmented -parts of the marginal bodies with as little injury to the adjoining parts -as possible. After the operation it seemed as if the intervals between -the pulsations were irregular,--not a series at regular intervals. An -hour or so after the operation the pulsations were very intermittent. -During the afternoon it was not seen to pulsate except when it was -stirred up, when six or seven vigorous pulsations followed. These, -however, were rather aimless. - -51. One sensory club (marginal body) was cut out, including its basal -part also. In one or two other cases more or less injury was done to -adjoining parts also. Pulsations ceased upon the removal of the last -club, but upon placing it in an aquarium and allowing it to come to rest -for two or three minutes, pulsations were now and then seen. In the -evening, this one and another did not pulsate except when stirred, when -they pulsated with good progress. - -52. A circular cut, about two inches in diameter, was made through -the epithelium of the subumbrella around the base of the oral lobes. -The animal pulsated well enough, but the contractions seemed not so -simultaneous in all parts of the margin as normally. After a few days it -had partly regenerated but died. One of the oral lobes cut off had some -power of contraction, and this some time after the operation. A similar -cut, but semicircular, made no difference between the contractions of the -two halves. - -53. The whole region of the sensory clubs was cut out when the animal was -not seen to pulsate again, except in the evening, when pulsations were -observed. The oral lobes also moved. - - - - -HISTOLOGICAL. - - -_Method._--The following results on the histology of the sensory clubs, -their eyes, and the tentacles, as already noted, were obtained from some -of Dr. Conant’s preserved material. These results relate almost wholly -to Charybdea, with only a few references to Tripedalia, noted in their -proper place. - -A portion of this material was killed after keeping the animals in the -dark for some time, for the purpose of discovering any changes in the -pigment of the eyes. I believe that a retraction of the pigment of the -long pigment cells that project between the prisms and pyramids of the -vitreous body in the retina of the distal complex eye is very evident in -eyes killed in the dark. (But more on this below.) - -I obtained my best results from the material preserved in saturated -corrosive sublimate, to which had been added (5 to 10 per cent.) acetic -acid. This also was Conant’s experience in his previous work on Charybdea -and Tripedalia. - -My best sections were obtained by embedding the sensory clubs in -celoidin, passing the little blocks of celoidin with the sensory clubs -into chloroform until perfectly transparent, and then into paraffine. I -then cut sections as we ordinarily cut paraffine sections, mounted and -stained them on the slide. My purpose in using this method was to avoid -the displacement of the vitreous bodies of the eyes during embedding -and cutting. This object was fully realized and more besides. Since the -sections cut by the celoidin-paraffine method gave me so decidedly the -best differentiation of the axial fibers of the retinal cells, as also of -the cilia, basal bodies, etc., I am inclined to believe that the celoidin -was in part responsible for this differentiation. - -Most of my series were cut 4 µ in thickness. All in all I cut sixty-five -clubs besides making some maceration preparations from material preserved -for that purpose. These sixty-five series represent material from -fourteen bottles. As a whole, my material was good, but the material from -one bottle was decidedly superior for showing the axial fibers of the -prisms and pyramids of the retinal cells. This shows the advantage of -plenty of material. It will be evident that I had plenty of material. - -I found iron-hæmatoxylin the most satisfactory stain. I stained for a -shorter or a longer time--one-half to several hours and longer--and then -washed out the sections until under a low power of magnification they -appeared quite unstained, the nuclei and a few other parts only appearing -darkly stained. - -Depigmentation I practiced but little. I obtained many of my series -almost wholly unpigmented, especially those I cut last. Others, of -course, were very heavily pigmented. I am not certain but that alcohol -slowly dissolves out the pigment after a long period of preservation. -Slight variations in the technique of killing and preserving may also, -perhaps, determine the stability or solubility of the pigment, as, of -course, also the condition of the pigment at the time of killing. - - -_Anatomy._--For a short epitome of the anatomy of a Cubomedusa and of a -Cubomedusan sensory club see p. 2 of the Introduction. - - -_The Distal Complex Eye_--_General_.--The distal (larger) complex eye -(Fig. 7) and the proximal (smaller) complex eye (Fig. 13) are so named -to distinguish them from the lateral simple eyes of the clubs. The -distal complex eye consists of the following parts: a cellular cornea, -continuous with the epithelium of the sensory club; a cellular lens -(externally cellular and internally often quite homogeneous) immediately -beneath the cornea; a homogeneous capsule just internal from the lens, -and evidently a secretion from the lens cells; a vitreous body composed -primarily of prisms and pyramids just beneath the capsule; and a retina -of pigmented cells, with subretinal nerve tissue, ganglion cells and -fibers. To my knowledge all observers (except Carrière, who missed the -capsule) are quite agreed on the anatomical structure of the distal -complex eye as also on the proximal complex eye and the lateral simple -eyes.[d] It is on the histological structure of some of the various parts -that differences exist. - - -_Cornea._--Little need be said on the cornea except that it consists -of flattened cells applied to the outer surface of the lens. It is -continuous with the epithelium of the club and evidently a modified -portion of this epithelium (Fig. 7). All observers conform to this -statement. - - -_The Lens._--The lens is of cellular origin, but in its interior -the cells are often so changed--absence of nuclei, cell walls, and -protoplasmic structure--as to make a mass quite homogeneous and -structureless. While this internal mass sometimes shows practically no -structure, yet at other times it is found broken up into masses much -the size and shape of cells but without nuclei, while again, cells with -nuclei may be quite evident. This occasional breaking up of this mass is -evidently predetermined by its original cell structure. Iron-hæmatoxylin -stains this inner mass very dark and it is difficult to wash out the -stain. Borax carmine and Lyons blue give the best results on the lenses. -In figure 7 the lens of the distal complex eye is shown as quite -homogeneous internally, while in figure 13 (proximal complex eye) it is -drawn cellular. In this latter lens the inner cells are quite round and -nucleated as they may also appear in the distal eye. What I have said -applies equally to the lenses of both complex eyes, though the cellular -nature of the inside of the lens is more readily demonstrated in the -proximal eye. - -It appears that it is in younger specimens that the central mass of -the lens shows the cellular structure best, and that as the animal -grows older this structure is more and more lost until no trace of it -remains. As concerns most of my series I could not well determine which -were from younger and which from older individuals, yet, several series -of quite small (5 mm.) and therefore young animals, in which the eyes -were so small that the lenses were compassed into less than half a dozen -sections, the cellular structure of the lens was very evident. - -The external cells of the lens form a spherical shell (both complex eyes) -which, in section, shows as a hollow ring (Figs. 7, 13). The thicker ends -of these cells lie at the inner (toward the capsule) half of the sphere -and the cells taper toward the corneal surface, dovetailing laterally -with their immediate neighbors as also distally with those from the -opposite side of the sphere. The thicker inner ends of the cells contain -the large nuclei with nucleoli. At a point (* Figs. 7 and 13) on the inner -(next the capsule) surface of the lens the cells only approximate each -other and thus leave a place which is easily broken through, as is shown -by portions (drops, probably representing cells or portions of cells) -of the mass within the lens becoming squeezed out into the substance of -the capsule and the vitreous body, and found occasionally also among the -cells of the retina. A considerable portion of the inside of the lens -may be found thus squeezed out, and its path can often be traced. This -phenomenon is evidently brought about by a contraction of the shell of -the lens during fixation and before the inside of the lens has become -hardened. - -In origin the lens is evidently ectodermal, originating from an -ectodermal invagination which becomes pinched off as a hollow sphere, -the outer (_i. e._ next the cornea) half of which becomes the lens, the -inner half the retina (_i. e._ vitreous body plus the so called retina). -(See Retina.) The transition from retinal to lens cells is quite readily -made out at the lower side of Fig. 7, but the corresponding structure on -the upper left side is not so manifest. It is further evident that the -lens is again an invagination into this sphere, and the point at which -the lens cells approximate (where the central mass of the lens may be -squeezed out as above described) represents the place of pinching off -of the original lens-retina sphere. It appears, then, that the lens is -formed in the lens-retina sphere in the following manner: The cells of -the secondary invagination going to form the lens begin to lengthen -distally (_i. e._ toward the cornea) during their invagination to form a -hollow sphere, at the same time dovetailing with each other and budding -off cells to form the inside of the lens (Figs. 7, 13). - -At the lower side of the lens, near the margin of the retina, the cells -of the lens are slightly indented or pushed inwards (Fig. 7, ind.). I -believe this to be due to the weight of the lens in the normal position -of the club, when the lens rests against the margin of the retina and the -capsule and adjacent tissue. - -Anticipating the description of the retina, it may here be added, that -the retina is formed from the inner half of the lens-retina sphere. The -cells of this portion of the sphere become differentiated into prism -cells, pyramid cells, and long pigment cells, while laterally, beyond the -margin of the vitreous body, they are differentiated into pigmented iris -cells (Figs. 7, 6a). - -Above are my results on the lens. Haake[2] speaks of the lens as -consisting of a cellular “Kern” with a covering of lamellated cells. -Carrière describes it as cellular and filled internally with a -“Gerinsel,” or coagulation. Carrière and Haake are each in part right. -Claus describes it as wholly cellular. Schewiakoff regards the lens as -wholly cellular, and like Claus has not noted that internally this cell -structure may be quite obliterated. Schewiakoff regards the lens and -retina as formed from an invaginated sphere, and shows the transition -from the lens cells into retinal cells as I have figured. Conant also -gives the structure of the lens for the complex eyes as cellular but -missed the change of structure that the interior of the lens may undergo. - - -_The Capsule._--The capsule of the lens (Figs. 4, 7) lies immediately -below (inward from) the lens. In structure it is homogeneous, except for -certain fibers from the long pigment cells of the retina that traverse -it, while sometimes also other fibers can be seen which, possibly, are -branches from the fibers just mentioned or continuations from the fine -fibers of the prism cells of the retina soon to be described. I have, -however, no evidence that the fibers from the prism cells extend beyond -the prisms in whose axis they lie. The capsule lies very closely applied -to the lens, never becoming separated from it in sections, and is, hence, -regarded as a secretion from the lens cells. Just what its function -may be is difficult to surmise. The proximal complex eye possesses no -capsule. I have thought, however, that if the lens should be adjustable, -the capsule might serve as a protection to the prisms of the vitreous -portion of the retina during the adjusting movements of the lens. (But -more on this below.) To my knowledge all previous observers are quite -agreed on the structure of the capsule. Carrière and Haake, however, -missed it altogether. - - -_Retina._--While I have enumerated (following previous observers) the -vitreous body and the so-called retina as distinct parts, yet, as the -sequel will show, they are, histologically, different parts of the same -thing--namely the sensorium proper of the eye--and I propose to use -the term retina for both taken together, while I retain the expression -vitreous body (as hitherto used) for the vitreous portion of the retina. -This simplifies matters; and using a word that is already used for -analogous structures of other eyes (vertebrates, anthropods, molluscs) -is conducive to clearness. I have been tempted, furthermore, to use the -words _rods_ and _cones_ for the prisms and pyramids that I find in -the vitreous bodies of the retinas of the complex eyes. But since the -prisms in reality approximate prisms and the pyramids pyramids, in their -shape, I have decided to retain the words prism and pyramid for these -structures. The former of these terms (prism) was first used by Conant in -his description of the complex eyes. - -What I shall call the retina, then, in the distal and proximal complex -eyes of Charybdea, consists of three kinds of elements: the prism cells, -the pyramid cells, and the long pigment cells. (Figs. 4, 7, 22, prc, -pyrc, lp.) We may also describe the retina as composed of three zones: -the vitreous zone (vitreous body of authors), the pigmented zone, and the -nuclear zone. (Figs. 4, 7, 22, vb, pz, nz.) - -The cells composing the retina form a single layer in the shape of a -hollow cup, into which cup the lens with its capsule fits. (Fig. 7.) This -single layer of cells takes in the thickness of the vitreous zone, the -pigmented zone, and the nuclear zone. Indeed, the distinctions vitreous -zone (vitreous body), pigmented zone, and nuclear zone characterize three -topographical regions of the retinal cells. - -That the retina is made up of three kinds of cells is most readily -demonstrated in transverse sections through the vitreous body. Fig. 1 is -such a section, taken quite near the pigmented zone (at about the level -x, Fig. 4). Three different kinds of areas are readily made out in such -a section. The more numerous areas (pr) are transverse sections of the -distal prisms of the prism cells, the less numerous and lighter areas -(pyr) are transverse sections of the pyramids of the pyramid cells, and -the large oval heavily pigmented areas (lp) are the transverse sections -of the long pigment cells. The dots within the two first named areas -represent fine fibers in the axes of the prism and pyramid cells, to -be described below. The presence of three kinds of cells can again -be readily seen in such Figs. as 4 and 7, in which the elements of -the retina are cut parallel to their long axis. (Fig. 22.) Again, a -transverse section through the most distal part of the pigmented zone of -a slightly pigmented retina (Fig. 2) also shows us the presence of three -kinds of elements. The larger and more heavily pigmented areas (lp) are -the long pigment cells; the smaller, lighter areas (pyrc) with a central -dot are the pyramid cells, and the more numerous dots, with no definite -polygonal areas outlined about them (prc), belong to the prism cells. -Thus, I believe, we have conclusive evidence of the existence of three -kinds of cells in the retina of the distal complex eye. - -(a) The prism cells are the more numerous, and, as the name implies, -end distally in a vitreous polygonal prism (Figs. 4, 7, 22, pr). The -prismatic structure of the vitreous body is also shown in Figs. 10 and -11, which are drawn from a macerated preparation of Conant’s. (See the -descriptions of these figures.) - -In Figs. 4 and 7 the prism cells correspond to the cells with the darker -nuclei (npr); in Fig. 2 they are represented by the dots without defined -polygonal areas about them (prc), and in Fig. 1 by the most numerous -areas (pr). These cells, then, consist of a centrad portion with nucleus, -a pigmented portion with granules of a dark-brown pigment, distal from -the nucleus, and a distal vitreous prism which extends to the capsule of -the lens. - -In the axis of each prism is a fine darkly-staining fibril extending -the entire length of the prism. I found no good evidence that this -fiber extends into the capsule. Centrad this fiber is continued through -the pigmented part of its cell and approaches to or near the nucleus -(Fig. 2, dots without defined polygonal areas; Fig. 7, part of retina -left unpigmented). In some instances I could trace this fiber quite to -the nucleus, while in others it ended before reaching the nucleus or a -little to one side of it. I am inclined to believe, however, that it -extends past the nucleus and is continued as a nerve fiber. I believe -this to be so because the fiber is evidently sensory, and _a priori_ we -should expect it to be so continued. Further, I find decided evidence in -sections of the simple eyes to show that the fibers there extend past the -nucleus into the subretinal tissue where I could not trace them farther. -(Fig. 16.) Again, that the flagella of the epithelial cells of the club -are also continued into the cells, in some instances could be traced past -the nuclei (Figs. 12 and 26), and the fact, too, that the retinal cups of -the eyes represent invaginated epithelium (the axial fibers of the prisms -are hence cilia?)--all this leads me to believe that the axial fibers -of the prism-cells extend centrad past the nuclei through their cells -and are continued as nerve-fibers. (See below under pyramid-cells and -under epithelium). Immediately upon entering the pigmented part of its -cell the axial fiber of a prism-cell has a dumbbell-shaped enlargement -which lies quite at the distal edge of the pigmented part of the cell -(Fig. 7, unpigmented part of figure). This, of course, can be seen only -in unpigmented retinas. This dumbbell-shaped body, (Basalkörperchen of -Apathy), which name I give it, since it evidently is homologous to the -basal bodies described by others for the cilia of epithelia, can be most -beautifully seen as two minute spheres lying close together and in line -with the nucleus. These two little spheres of the basal bodies put to the -test the highest powers of the microscope; but, when, after a prolonged -and careful study, one satisfies himself of their existence and exact -shape, the very difficulty with which they are resolved adds a zest to be -appreciated. The length of a basal body is about one-fifth to one-fourth -that of the nuclei of the prism-cells. - -The structure of the nuclei of the prism-cells is that of a dense network -(Figs. 4, 7, npr) which stains dark with hæmatoxylin. A nucleolus can -often be seen in these nuclei. In some few series, again, these nuclei -did not show a network-like structure, but the chromatin was arranged in -masses (Fig. 5, npr). These nuclei can usually be distinguished from -those of the other cells of the retina by their denser, darker-staining -network (Figs. 4, 7, npr), or as shown in Fig. 5 (npr). Their denser -structure and staining capacity are a distinguishing characteristic of -the nuclei of the prism-cells. I must add, however, that not in every -series is this apparent. - -That portion of a prism-cell that contains the nucleus rarely contains -any pigment; and when pigment is present, I believe that it has been -dissolved in from the pigmented zone. The nucleus, again, lies a little -centrad from the pigmented part of its cell, so that an unpigmented zone -is seen in the retina between the pigmented zone and the row of nuclei -(Figs. 4, 7, 22). - -Centrad the prism-cells are continued as a single process (Figs. 6, b, -c, d, and 8a, b, c, d). In some sections I thought I could trace these -processes to the basement membrane, but I could not satisfy myself that -such appearances were not due to artificial splitting in the tissue. -Schewiakoff makes a similar remark about his supporting cells, which -cells I believe are the same as my long pigment cells, but these do not -extend to the supporting lamella. - -At the margin of the retina the cells do not develop prisms but remain -pigmented and form an iris (Fig. 7), which was so named by Claus and also -described by Schewiakoff. These cells also assume a somewhat different -shape (Fig. 6a). This cell (Fig. 6a) is seen from its broader side with -which it is applied to the capsule or the lens. Schewiakoff figures -similar cells. That the cells of the iris are prism cells without the -prisms does not necessarily follow. They simply represent cells of the -retinal cup that have become differentiated to serve as an iris. - -As to the exact origin of the prisms, and pyramids (to be described -below), it is difficult to say anything definite. If the so-called basal -bodies of the axial fibers are really homologous with the basal bodies -of flagella, then it would seem that they (the prisms and pyramids) are -secretions comparable to cuticular secretions. - -(b) The pyramid-cells, like the prism-cells, are differentiated into -three regions: a distal vitreous pyramid, a pigmented part, and a centrad -part with nucleus. The pyramids are seen in transverse section in Fig. 1 -(pyr) and in longitudinal section in Figs. 4 and 7 (pyr).[e] - -Each pyramid extends between the bases of the prism-cells about one-third -to one-half the depth of the vitreous body (Figs. 4, 7, 12 (pyr)). The -pyramids are also a shade lighter than the prisms, which fact is -characteristic. In the axis of each pyramid is a darkly-staining fiber -quite like the one described for the prism-cells (Figs. 1, 4, 7, 22). -That this fiber extends distally beyond the limits of the pyramids I -could not determine, but I do not think that it does. Centrad this fiber -extends into the pigmented portion of its cell quite to or near the -nucleus as was described for the fibers of the prism-cells (Figs. 7, 22). -Whether or not these fibers extend past the nucleus and become continued -as nerve fibers, the same course of reasoning holds as was given for the -fibers of the prism-cells. Each of these fibers possesses a basal body -just on its entrance into the pigmented part of the cell (Fig. 7), but -I could not determine that it was dumbbell-shape. In form it represents -an enlargement of the fiber itself, which gradually tapers again to its -normal size. The continuations of these fibers within the pigmented -parts of the pyramid-cells, as also the basal bodies, could only be -demonstrated in unpigmented series. - -Patten[5] describes axial fibers extending centrad through the rods -(vitreous portions) of retinal cells (“retinophora”) into the region -of the nucleus and past the nucleus (arthropods and molluscs). My -retinal cells (prism and pyramid cells) evidently correspond to Patten’s -retinophora, but I find no evidence that one of my retinal cells -represents more than a single cell, while Patten gives evidence that -his retinophora are made up of two cells closely applied to each other -as twin cells. If this were also true for the retinal cells that I have -described, I believe my macerated preparations would have shown it. -Schreiner[12b] and Hesse[13] also figure and describe axial fibers for -the rods of the visual cells in polychætous annelids, and Schreiner[12a] -also for molluscs. Neither of these observers finds the fibers to extend -distally beyond the rods nor centrad toward the nucleus as Patten and -myself show. Neither Schreiner nor Hesse figures these cells as twin -cells as Patten does, so that to my knowing Patten stands alone in this -respect. Andrews[14] describes and figures rods for the visual cells of -polychæte annelids but no axial fibers. He was the first to describe -these rods in annelids. - -The pigmented zone of the pyramid cells, in heavily pigmented series, is -filled throughout with dark-brown pigment granules, and is quite like -that of the prism cells (Figs. 4, 7). In transverse sections, however, -through the most distal part of the pigmented zone, of unpigmented -series (Fig. 2), lighter areas with central dots could occasionally be -demonstrated, which areas are the pyramid cells. In Fig. 2, the more -definite polygonal outline as well as the lighter shade of these areas -was a distinguishing feature. The difference in shade was not wholly due -to a difference in pigmentation but to a structural difference. - -The nuclei of these cells are usually a little larger than those of the -prism cells and are filled with a finer and less dense network (Figs. 4 -and 7, npyr), in consequence of which they present a lighter appearance -in sections when examined with a high power. It will be seen in the -figures (4, 7) with what regularity these lighter nuclei lie opposite -the pyramids. Some few exceptions occur. These are probably due to the -fact that a nucleus or pyramid was not differentiated by the technique. -If this opposition between the pyramids and the lighter nuclei were all, -I believe it would be sufficient evidence for associating these lighter -nuclei with the pyramid cells.[f] - -(c) The _long pigment cells_ are about as numerous as the pyramid cells. -In these cells, as in the prism and pyramid cells, three regions can be -distinguished: the region of the nucleus, a pigmented region (the distal -half of which extends between elements of the vitreous body), and a -distal rod-like portion, or fiber, which is continued between the prisms -into the capsule of the lens (Figs. 4, 7, 9). The pigmented portion is -about twice the length of that described for the other cells, and also -often of greater diameter, so that in transverse sections (Figs. 1, 2, 3) -these cell-areas are larger than those of the other cells. As nearly as -I could determine, these cells are pigmented just like the other retinal -cells described. In quite unpigmented series, however, they often contain -more pigment than the other cells do (Fig. 2). Distally, the pigmented -part becomes narrowed to a strong pigmentless fiber (Figs. 3, 4, 7). This -fiber stains quite dark with iron-hæmatoxylin and appears homogeneous. It -passes between the prisms into the capsule, where it usually bends in a -direction toward the margin of the capsule (Fig. 7) and passes diagonally -across this to the lens. In sections, a space is often seen about these -fibers in the vitreous body, which I regard as a shrinkage space (Figs. -3, 4), since it is not evident in all series (Fig. 1). In Fig. 7, I have -assumed that these spaces are due to shrinkage and have not indicated -them. Also, in this same figure I have assumed that the spiral appearance -of the fibers (Fig. 4) is due to a shortening of the prisms during -fixation, and have drawn them straight. At the lens these fibers seem -to end. In a few instances they were seen to branch upon reaching the -capsule (Fig. 4). In Fig. 9, also, which shows some of these cells from -a macerated preparation by Conant, the rods show evidence of branching -at their distal terminations. In the same preparation I thought I could -see that a fiber became expanded into a membrane spreading over one of -the lens-cells. I could not satisfy myself, however, that this was the -actual condition of things. Judging from Fig. 9, one might conclude that -all the fibers are branched distally; yet, if such were the case I should -have seen more of it in sections, but branching as seen in Fig. 4 is the -exception. Hence, if all these fibers do branch, I am inclined to believe -that it must be among the bases of the lens-cells. Or, if the fibers -do expand into membranes to cover the lens-cells (I could not explain -purpose), the evidence in Fig. 9 may be nothing more than fragments of -this membrane left attached to the ends of the fibers. As is seen in Fig. -7, most of these rods end opposite the cells of the lens, and not usually -between two adjacent cells as Schewiakoff has described for Charybdea -marsupialis. The nuclei of these cells are like the nuclei of the pyramid -cells (Figs. 4, 5, 7, 9) and often have a nucleolus.[g] Centrad these -cells are continued into a number of processes as is seen in Figs. 5, 7 -and 9. How far the several centrad processes extend and where they end I -cannot say; but, as seen in Fig. 5, they soon taper to a thin end which I -suppose may be continuous with a nerve fiber. I believe Schewiakoff was -mistaken when he stated that these cells extend to the basement membrane. - -I have found no evidence in these cells of the existence of an axial -fiber such as I have described for the prism and pyramid cells. I find no -definite arrangement of the nuclei of the retina into definite layers, -but the nuclei of the three kinds of cells lie quite mixed, sometimes one -kind lying deeper than the other as can be seen in the figures. Again, -they may lie quite at the same level. (This point will be referred to -later.) - -It is these long pigment cells that I believe retract their pigmented -part from between the prisms and pyramids when the medusæ are placed in -the dark, protruding with their pigment when placed in the light. Fig. -5 is a section from a slightly pigmented retina killed in the dark. The -parts of the cells projecting beyond the pigmented zone, and which would -lie between the prisms and pyramids (here not shown) of the vitreous body -are seen to be narrower than in sections from retinas killed in the light -(Figs. 1, 3, 4, 7) and the cells themselves appear in a condition of -retraction as is shown by their large centrad portions with the nuclei, -which latter, also, here lie at quite a lower level than the other -nuclei. (The pyramid cells were not shown in this series.) I occasionally -found appearances like Fig. 5 in retinas killed in the dark (indeed, -in some the pigmented portions in the vitreous body were much thinner -and more retracted than in Fig. 5). Yet this appearance was not of -sufficiently general occurrence to leave no doubt as to its significance. -As positive evidence, however, I cannot give it any other interpretation -than the one given--that the cells retract themselves with their pigment -when in the dark. Again, it must be added that the nuclei of these cells -may occasionally lie quite deep even in retinas killed in the light. -Indeed, like structures in different retinas may vary considerably in -size and shape. None of my darkness retinas, however, showed such a large -proportion of the pigmented parts of the long pigment cells projected -between the prisms and pyramids as did the light retinas. I examined -and tabulated all my series with respect to the extent the long pigment -cells were projected into the vitreous body, and I found that those which -showed these cells with their pigment least projected between the prisms -and pyramids to be those that had been killed in the dark. I thus feel -satisfied that the pigmented parts of these cells become in part or quite -completely retracted from between the prisms and pyramids of the vitreous -body when in the dark, but just how this is accomplished--whether -the whole cell with its nucleus takes up a deeper position, the cell -substance at the same time collecting in the region about the nucleus, -as shown in Fig. 5 and the diagram (Fig. 22), I cannot with certainty -state. It would seem, too, as though the pigment became less in the cells -exposed to darkness, for I rarely, even in the most retracted heavily -pigmented series, saw the pigment to extend farther towards the nucleus -than commonly. The time of keeping in the dark, prior to fixing, varied -from three-fourths of an hour to one and one-half hours. I could not -bring the amount of retraction into relation with the time of exposure, -except that in general the retinas longest exposed showed the greater -amount of retraction. - -(d) The tissue underlying the retina is described by former observers -(Claus, Schewiakoff, Conant) as composed of nerve-fibers and ganglion -cells. I cannot give it any other interpretation, but I must add that -the supposed ganglion cells are seen only as nuclei, no cell bodies ever -being demonstrable in any of my sections. Conant also recognized no cell -bodies. Occasionally, as in Fig. 7, long fibers could be traced for some -distance in this subretinal tissue, in some instances quite to or from -a visual cell. Pigment was not regularly observed in this tissue, as -Schewiakoff describes, and when present I believe it has been dissolved -in from the pigmented zone. - -(e) Schewiakoff describes the retina (my pigmented and nuclear regions) -as composed of spindle-shaped visual cells (my pyramid cells?) -alternating with pigmented supporting cells (long pigment cells), with -the nuclei of the former lying more centrad than those of the latter. -The visual cells are pigmented only at their periphery, or surface, -leaving an unpigmented axis, while the supporting cells have pigment -throughout their whole substance within the pigmented zone. Distally, -the visual cells have hyaline rods, or fibers, which extend into spaces -in the vitreous body, and pass through this and the capsule to the lens. -The vitreous body is described as homogeneous, except the spaces for the -visual rods, and a secretion from the retinal cells. - -It will thus be seen that my results are quite different from those -just described. I find the vitreous body to be composed of prisms and -pyramids with axial fibers, while the long pigment cells (supporting -cells of Schewiakoff) are continued into the vitreous body, and becoming -narrowed into a non-pigmented fiber, extend to the lens as described. -The prisms and pyramids are, further, the distal continuations of cells -whose pigmented and nuclear parts lie in the so-called retina, but which, -together with the vitreous body, I have named the retina proper. Conant -has so summarily disposed of Schewiakoff’s distinction between retinal -cells based on pigmentation and location of nuclei, that I need not say -more. Schewiakoff’s Fig. 18 corresponds to my Fig. 1. In this figure he -shows the vitreous body as homogeneous with pigmented areas (my long -pigment cells) and with spaces with his visual rods. It is quite evident -that his spaces with the visual rods correspond to my lighter areas with -central dots; _i. e._ my pyramids of the vitreous body are the same as -the spaces shown in his Fig. 18. It is quite evident that Schewiakoff -mistook the lighter areas for spaces. That they are not spaces can -readily be seen by comparing them with real spaces. It is, of course, -possible, too, that the reagents had dissolved the pyramids, leaving -only the axial fibers with a little pyramid substance about them, and -that this is what Schewiakoff saw. I often found small circular spaces -in the centers of the pyramid areas, as also in the prism areas (Fig. -3), which might be taken for hyaline visual rods, fibers, in transverse -section, but in such spaces I could usually see a small dot to one side -of the space that I take to be the rod (fiber) proper. Fig. 14 also -shows such small circular spaces that have very much the semblance of -hyaline rods. This figure is a transverse section of the vitreous body -of the proximal complex eye, in which no long pigment cells or pyramid -cells are present, but it serves well to illustrate the point. The above -explanation also accounts for the large size of the visual rods (fibers) -in Schewiakoff’s figures. That the fibers of the pyramid cells (visual -rods of Schewiakoff) do not extend to the lens is quite evident in my -Figs. 4 and 7. - -Again, since the long pigment cells are often not seen to terminate in -a fiber, but a part of the fiber can often be seen in the distal part -of the vitreous body and in the capsule, it will be quite readily seen -how Schewiakoff should associate his visual rods, or fibers, with these -distal parts of the fibers of the long pigment cells and suppose his -visual rods to extend to the lens. - -Again, since the long pigment cells sometimes cannot be seen to terminate -distally in a fiber, while the vitreous body at the same time may be -broken away from the pigmented zone (Fig. 4), it is quite evident how -Schewiakoff should have interpreted the parts of the long pigment cells -in the vitreous body as conical pigmented caps placed opposite his -supporting cells (long pigment cells). - -Finally, since Schewiakoff had only twelve marginal bodies to study, and -since this tissue is difficult to preserve properly, I do not believe -that I am doing Schewiakoff any injustice by explaining away his results -as I have done. This fact remains, that Conant and myself agree in all -points in which we differ from Schewiakoff. - -To Conant belongs the credit of having first demonstrated the prismatic -structure of the vitreous body, and he also regarded the prisms as a -part of the retinal cells. H. V. Wilson[15, 8b] suggested, however, some -years prior to Conant, that the vitreous body might be of a prismatic -structure. Conant had evidence also of both the prism and pyramid fibers, -as is well shown in his figures of transverse sections but he found -his evidence too meager to make any very definite statements. Indeed, -Conant concludes that there are three kinds of fibers in the vitreous -body and complains of finding but two kinds of cells in the so-called -retina (pigmented and nuclear zones) to which to refer them. He saw the -pyramids with their axial fibers as lighter areas in transverse sections -of the vitreous body (his Figs. 64 and 68, and my Figs. 1, 4 and 7), but -suggests that they may be the same as the long pigment cells, the cells -having only to project themselves or their pigment in order to become -long pigment cells. This suggested to him to preserve material both in -the light and in the dark. I do not think Conant’s supposition to be a -fact, for I find the pyramids in specimens preserved in the light as well -as in the dark. It is, of course, possible that the pyramid cells are in -a stage of structural transition to the long pigment cells, for, besides -their pigmentation, they also have like nuclei. Furthermore, I held for -a long time with Conant that there may be only two kinds of cells in the -retina, but I soon found the pyramids so definitely shown as to leave no -doubt but that they represented a third kind of cell. For me it remained -to first definitely see all the fibers in the vitreous body as also the -pyramids in sagittal sections. - -Conant describes the long pigment cells with their fibers extending -between the prisms of the vitreous body quite as I have described, and -in this my work is only confirmatory of his. Conant does not, however, -describe the several centrad processes of these cells, nor is he clear -that their distad processes extend to the lens, though he speaks of -fibers within the capsule. - -(f) What, now, is the function of these three varieties of cells of the -retina? Schewiakoff regards his visual cells (pyramid cells), as the -name implies, as having a visual function. That they have such it seems -reasonable to suppose, since they have an axial fiber in their pyramids. -If the pyramid cells are visual cells, it appears that the prism cells -also are such. Indeed, since these are the only ones present in the -proximal eye and the more numerous ones in the distal eye, and like the -pyramid cells have an axial fiber in their prisms, it seems that they -are the visual cells _par excellence_ of the Cubomedusan eye. Also, the -analogy between the prisms and pyramids on the one hand, and the rods and -cones of the vertebrate eye on the other hand, does not seem to be so far -fetched. It may be of interest, here, to briefly consider Patten’s theory -of color vision.[5b] - -The gist of Patten’s theory is this: In the eyes of certain molluscs -and arthropods, in the parts of the retinal cells corresponding to my -prisms and pyramids, he not only finds an axial fiber (or fibers) but -finer fibrils that extend at right angles from these axial fibers to the -surface of the rods (I shall here, for convenience, call the prisms, -pyramids, etc., rods) where they probably become continuous with other -fibrils in the surface of the rods. These fibrils from the axial fibers -are arranged in superimposed planes, and if I understand rightly, an -axial fiber with its radiating fibrils may be compared to the axial -wire with its radiating bristles of a brush used for cleaning bottles, -provided the bristles of such a brush be arranged in superimposed -planes. The lateral arrangement of the fibrils will, of course, be -modified according whether a rod is circular, hexagonal, square, etc., -in transverse section. It will also be remembered (p. 49) that Patten -describes the retinal cells studied by him as composed of twin cells, -and he gives the name _retinophora_ to a pair. The system of fibers and -fibrils in the rods he names a _retinidium_. Centrad the axial fibers -are continued past the nucleus as a nerve fiber. The fibrils extending -laterally in superimposed planes from the axial fiber of a rod, Patten -supposes to be the ones stimulated by the incoming rays of light, the -retinophora being so arranged that the light rays entering them are -parallel to the axial fibers or perpendicular to the lateral fibrils of -the retinidium. Again, since the rods are usually the shape of truncated -pyramids or cones the lateral fibrils, which are perpendicular to the -axial fibers, are of different lengths accordingly as they are situated -at the larger or smaller end of a rod. Patten assumes similar fibrils to -exist in the rods and cones (particularly the cones) of the vertebrate -eye, and he thus makes a general application of his theory. He supports -himself in this rather sweeping generalization by the claim to have -demonstrated the twin-cell nature of the cones in amphibia and fishes. - -For illustration, Patten supposes that if red light only were admitted -to the retinophora this would stimulate the fibrils near the broader -end of the cone (but that all the fibrils of the retinidium would be -stimulated a little) and that we would thus have the sensation of red -light. Likewise, if violet light only were admitted, the fibrils at the -narrower end of the cone would be stimulated, and we should have violet -light. Similarly, if light including all the different wave lengths of -the spectrum were admitted, all the lateral fibrils would be stimulated -and the sensation of white light produced. The method of stimulation need -not be that of a vibration of the fibrils. - -Certain grave objections may be raised against such a theory, the most -serious, perhaps, being the fact that no such fibrils as Patten has -described have as yet been demonstrated for the eyes of those animals -that we know have color vision. Yet, as a whole, the objections are -perhaps no more serious than any that can be brought against other -theories of color vision. What Patten’s theory does do,--it gives us -a definite mechanical basis to work from, and if these fibrils should -be demonstrated for the rods and cones of vertebrates, physiologists -would then have a mechanical basis for color vision quite as they now -have for hearing. As Patten says, the problem is primarily a mechanical -one. However, the theory cannot well pass for more than a suggestion, a -stimulus for future work, and in this lies its present value. - -It is quite evident that my results for the retinal cells of Charybdea -are, if any thing, a support to Patten’s theory. While I have not been -able to demonstrate the fibrils that are the essential to Patten’s -theory, yet I have demonstrated the axial fibers of the rods, and if -these fibers should be continued as a nerve fiber to some central -ganglion (as I believe is reasonable to suppose, see p. 47), I do not -see how we can avoid the conclusion that these axial fibers of the prism -and pyramid cells are somehow concerned in vision. In Patten’s theory -these fibers would represent a conducting element, the real sensory -element (fibrils perpendicular to these axial fibers) not having been -demonstrated by me. - -I have recently read in a short review of Patten’s theory[9] that the -evidence we at present have points to the tips of the cones (vertebrate -eye) as being the seat of the sensation of red. This would be exactly the -converse of what Patten’s theory supposes. Whether or not this objection -is a real one, future investigation only can determine. - -Hesse[13] regards the axial fibers that he describes for the rods in -worms as the primitive fibers of Apathy. In this I agree with him, -regarding the axial fibers I have described as “Primitivfibrillen.” -Further, I believe, if I understand Apathy rightly, that the fibrils -described by Patten as extending laterally from the axial fibers -correspond to Apathy’s “Elementarfibrillen.” - -It is the long pigment cells that are the puzzling element. Since there -can be little doubt but that these cells can project and retract their -pigmented parts (as already described), it would seem that a part of -their function is to check the diffusion of light in the vitreous body -when exposed to strong light. This function would be quite analogous to -that of the pigmented cells of the vertebrate retina, which in light -become projected between the rods and cones. Similar observations have -also been made on the compound eyes of arthropods by Herrick[10] and by -Parker[7], who find that the distal retinula cells of Palæmonites project -themselves distad in the dark, thus surrounding the vitreous cones with a -cylinder of pigment, while (Parker) the pigment of the proximal retinula -cells migrates centrad and the accessory cells move distad; in light the -reverse takes place. Other observations of this kind are not wanting for -crustacea, insects and arachnids. To my knowledge, the pigment changes -that I have described are the first of their kind for medusæ. - -I suggested while describing the capsule, that the lens might be -adjustable. That the fibers of the long pigment cells extend to the lens -is my principal reason for this. May these cells not represent ganglion -cells and their distad fibers nerve fibers? That they are not sensory -(_i. e._ are stimulated by light waves) seems to be suggested by their -not having any axial fiber and in having several centrad processes. -These facts suggest that they are not sensory but the center of a reflex -mechanism.[h] When the sensory cells proper are stimulated, the impulses -are conducted centrad into some nerve center (it may be the nerve tissue -underlying the retina, or other nerve centers such as the two groups of -ganglion cells in the upper part of the club, or the radial ganglia) -from which center, again, impulses return over fibers leading to the -long pigment cells causing them to project their pigment, and conducting -the impulse to the lens, to produce a change in its adjustment. Since -these cells are not so numerous as the prism and pyramid cells taken -together, but in turn have a number of processes continued centrad (the -sum of which processes approximates the number of sensory cells, prism -and pyramid cells) it appears that these cells are admirably adapted to -function in just such a mechanism as I have described,--each long pigment -cell serving a number of its immediate neighbors. - -Further, we may conceive each of the centrad processes of the long -pigment cells as receiving a fiber from one of the sensory cells directly -as well as indirectly, as just described. While I have been able to -demonstrate only a single centrad process for the sensory cells (prism -and pyramid cells), yet this does not exclude the possibility of a nerve -fibril passing out from such a centrad process to one of the processes -of the long pigment cells, and it seems possible that this constitutes -the reflex mechanism. That nerve fibrils ramify in ganglion and sensory -cells, and may even leave these cells to join those of other cells, has -been well demonstrated by Apathy,[6] so that my finding only a single -process of the visual cells leading centrad without giving off lateral -fibers cannot be a serious objection. Again, fine nerve fibers coming -off from the main centrad process of sensory cells in medusæ have been -figured by other observers, among whom I mention the Hertwigs. Careful -macerations at the seashore would probably demonstrate them for Charybdea. - -Hesse thinks that the eyes of the Alciopidæ are adjustable. He describes -what he supposes to be muscle fibers just exterior (distal) to the lens, -and believes that a contraction of these fibers would have the effect of -forcing the lens nearer the retina, or _vice versa_. His supposition, -like mine, needs experimental verification. Hitherto the only instance -known of accommodation in the eyes of invertebrates was that described by -Beer[17] for Cephalopods. - - -_The Proximal Complex Eye._--With four exceptions, the description and -discussion given for the distal complex eye also holds good for the -proximal complex eye (Fig. 13). The four exceptions are: the absence of a -capsule to the lens; the absence of the long pigment cells; the absence -of the pyramid cells; and the different relative position of the lens -and retina. This eye, then, has a cornea continuous with the epithelium -of the sensory club, a lens, in structure and probable origin quite like -that described for the distal complex eye, and a retina of prism cells -with axial fibers for the prisms. Since Conant[8b] has described this eye -quite fully, and discussed Schewiakoff’s conclusions at length, I shall -be brief. Suffice it to say, that Schewiakoff describes two kinds of -cells (supporting cells and spindle-shaped visual cells) for the retina -of this eye just as he described for the distal complex eye. The vitreous -body he likewise describes as being homogeneous and with spaces for the -visual rods (fibers) of the visual cells. It is evident that Schewiakoff -has interpreted the structure of this eye from analogy with his results -on the distal complex eye. Claus likewise has described two kinds of -cells for the retina, and the vitreous body as homogeneous. Conant -and myself find only one kind of cells in the retina of this eye. The -pigmentation that Schewiakoff describes for the vitreous body I believe -to have been dissolved in from the pigmented zone of the retina, for I -find no regular pigmentation in the vitreous body. Haake’s observation, -previously noted (p. 42), applies also to the proximal complex eye. - -Conant’s evidence for the axial fibers of the prisms was clearly -insufficient, so that he did not in this respect complete his Fig. 69. I -republish this figure with the prism fibers drawn (Fig. 13). - -Since the long pigment cells are absent my reasons for supposing the lens -of this eye to be adjustable vanish. - -Finally, a word on the origin of the lens and the relative position of -the lens and retina. The lens and retina in this eye are evidently -not developed from an outer and an inner half, respectively, of the -invaginated and pinched-off lens-retina sphere (as is true for the distal -complex eye) but from proximal and distal halves respectively. It is also -quite easy to understand the connection of the lens in this eye with the -supporting membrane. Since the cells of the ectoderm of the club can in -many instances be seen to extend to the basement membrane, or supporting -lamella, the cells of the lens, which arise from the ectoderm, simply -remain in connection with the basement membrane, this becoming thickened -to form a support for the lens. That the lens of the distal complex eye -has lost its connection with the basement membrane is evidently due to -the fact that the lens is formed from the outer half of the lens-retina -sphere. The cells of the lens are by this so far separated from the -basement membrane as to lose their connection with it. Schewiakoff also -notes the fact that the lens and retina of the proximal complex eye are -developed from proximal and distal halves of the lens-retina sphere. He -further supposes that the portion of the basement membrane that acts -as a support to the lens takes the place of the capsule in the distal -complex eye. This latter supposition I do not think probable, since the -supporting lamella does not form a distinct covering to the lens on its -retinal side. - - -_The Simple Eyes._--Since the shape and position of these eyes have -already been described (Claus, Schewiakoff, Conant), I shall not tarry -long in this respect. Speaking generally, these eyes are flask-shaped -(Fig. 12), the proximal pair quite so, while the distal pair are drawn -out in the transverse diameter of the club. These eyes are invaginations -of the surface epithelium and the shape of the cells lining these -invaginations is quite like that of the epithelial cells, except that -their distal portions (bordering the lumen of the invagination) are -heavily pigmented. The proximal walls (Fig. 12, left side) of the distal -pair are heavier pigmented than the distal walls and the proximal pair -of eyes. Schewiakoff calls attention to this point. The pigmentation is, -furthermore, not only heavier, but the pigmented portion of each cell is -much longer in the proximal walls of the distal eyes (indeed, the cells -are longer) than in the distal walls. The significance of this I do not -understand. Indeed, I am inclined to believe that in life all these eyes -are pigmented quite alike and that it is the reagents used that alter or -dissolve the pigment in certain places. Yet, the fact that the cells -of the proximal walls of the distal eyes have their pigmented portions -nearly double the usual length, shows some deeper significance. - -I also note here the small secondary, non-pigmented invagination into -the tissue of the clubs from each of the distal simple eyes. Schewiakoff -describes this invagination, and it extends in a proximal and dorsal -direction (dorsal-side of club opposite complex eye) from the dorsal -sides of the distal simple eyes. The cells of these invaginations are -not pigmented, but quite like the other pigmented cells in shape, and -like these with distal flagellate fibers. I do not see the necessity -of assuming, however, that these secondary invaginations are the real -sensitive parts of these eyes, while the pigmented parts serve as an -iris, as Schewiakoff does in his general discussion. - -The histological structure of both pairs of simple eyes is the same. -Sections and macerations give me evidence of only one kind of cells, -all pigmented alike (except, of course, the non-pigmented secondary -invaginations just noted). The cells in these eyes are very closely -crowded so that their nuclei lie at several different levels. That they -all extend to the lumen of the eyes and are all pigmented could be -demonstrated with certainty in many sections, when some of these cells -whose nuclei lay most centrad could be followed with the greatest nicety -to the lumen (Fig. 12). Macerations (Figs. 8, unlettered cells 21) also -show cells with very long cell bodies pigmented at their distal ends and -occasionally with a distal process or fiber. While there are, therefore, -spindle-shaped cells found, yet they are in every other respect alike, -and their differences of shape and position of nuclei are simply the -result of crowding. There is, therefore, no evidence of supporting -(pigmented) cells and spindle-shaped visual cells (pigmented only -externally) as Claus and Schewiakoff have described and which Conant and -myself cannot corroborate. - -Distally, the retinal cells of the simple eyes have each a fiber -(flagellum) that extends into the lumen (Figs. 12, 15, 16, 21). Each -flagellum has a dumbbell-shaped basal body just on its entrance into -its cell quite like the basal bodies described for the visual cells of -the complex eyes (Fig. 12, part left unpigmented). Each flagellum, or -fiber, can usually be seen to extend into the cell. In one series I found -appearances like Fig. 16, which is a drawing of a part of a section -through one of the proximal simple eyes. This section is quite in the -angle between the proximal complex eye and the group of network cells in -the upper part of the club. In this series I could very definitely trace -the distal fibers of the retinal cells centrad, past the nucleus and into -the subretinal nerve-tissue. These fibers could be so easily followed -that no doubt can exist as to the fact noted. It thus appears that the -axial fibers just described pass centrad through the cells and are -continued as nerve fibers. On the evidence of such sections as Fig. 16 I -have indicated these fibers as extending centrad through their cells. The -lumen of the simple eyes is filled with a homogeneous vitreous secretion. -This is often incomplete in some parts; occasionally the secretion -shows a formation of globules, but all this I believe to be due to the -action of reagents. Indeed, I have found simple eyes in which hardly any -secretion was present, while others showed an almost completely filled -cavity. In that portion of the vitreous secretion just outside the mouth -of the distal eyes I occasionally found numbers of very darkly staining -granules. I suspect that these are either bacterial or algal organisms. - -As already noted, Claus and Schewiakoff describe two kinds of cells -for the retinas of these eyes which neither Conant nor myself can -demonstrate. Further, I believe I have shown that only one kind exists. -If any doubt should still exist, a section like Fig. 25 (which is from -the epithelium of the club, but similar smaller areas with central -dots could often be demonstrated in transverse sections of the retinal -cells of the simple eyes) I believe should be convincing. Schewiakoff -further describes flagella for the retinal cells (his visual cells) of -the simple eyes quite as I have described them for all the cells. The -pigmentation that Schewiakoff mentions as occurring in the secretions -within the lumina of these eyes I believe to have been dissolved in from -the pigmented zones. I find no definite pigmentation in these vitreous -secretions. These secretions are evidently products of the retinal cells -and have been so regarded by former observers. - - -_Lithocyst and Concretion._--The cavity filled by the concretion is -lined in places by a single layer of cells, two of which are shown in -Fig. 7. This fact has been noted by both H. V. Wilson and Conant. Such -cells are evidently remnants of the cells that formed the concretion. The -supporting lamella completely surrounds the cavity of the concretion. - -The concretion filling the lithocyst has the shape of a hemiprolate -spheroid cut in the plane of the axis of revolution. Whether it is of -endo- or of ectodermal origin, I believe developmental studies only can -determine. Tests made in the Chemical Laboratory show the presence of -calcium sulphate with perhaps a very small trace of phosphate.[i] Nitric -acid slowly dissolves these concretions, but I believe Claus was mistaken -when he said that they dissolve with an evolution of gas. I watched -them dissolve under the microscope, and never could see the least bit -of gas formed. If Claus’s observation is correct, then the composition -of the concretions of C. marsupialis is different from that of the -concretions of C. Xaymacana. The concretions, further, were dissolved out -of the material preserved in formaline and in osmic acid solutions. For -dissolving them in situ I used either nitric or hydrochloric acid, or -both. A slight husk remains after all the lime is dissolved. - - -_The Epithelium of the Clubs._--The epithelium is thickest on the dorsal -side of a club. The thickening here, as in several other places, seems -to be due to a crowding of the cells, in consequence of which the nuclei -come to lie at different levels, but I believe that all the cells quite -reach the surface. The cells with their nuclei nearest the surface are -pyramidal in shape, with the bases of the pyramids toward the surface, -while those cells whose nuclei lie deeper (where several layers of nuclei -occur) may be spindle-shaped (Figs. 12, 23, 24, 26). Centrad these cells -are continued into a single process, which often seems to extend to the -basement membrane (Figs. 7, 12, 13, 23, 24). Where the epithelium covers -the region of the concretion, the cells become flattened and with the -long axis of their nuclei parallel with the surface of the club (Fig. 7). -The same holds true for the corneal epithelium (Figs. 7, 13). - -It is a significant fact that in many places the nuclei form only a -single layer, and in such places one cannot speak of spindle-shaped -cells. I cannot find any evidence of sensory and supporting cells as -Schewiakoff describes. The fact that spindle-shaped cells may exist is -simply a physical consequence of their being closely crowded. Conant -arrived at the same conclusion. - -But I have another and better reason for supposing the existence of only -one kind of cells in the epithelium. In a tangential section taken just -through the tips of the epithelial cells (Fig. 25) I find polygonal areas -with a central dot. This section does not at all agree with Schewiakoff’s -Fig. 8, in which he figures two kinds of cells. In Fig. 25 there can be -no evidence of two kinds of cells, unless both kinds have like flagella, -for these dots are the transverse sections of flagella continued within -the cells (Fig. 26). - -The epithelium, then, is flagellate, a flagellum to a cell. Whether there -are flagella on the epithelium covering the region of the concretion, I -could not determine. But I believe that in all other parts, excepting, -of course, the corneas, it is flagellated. The fibers (flagella) of the -simple eyes are evidently the flagella of the invaginated epithelium. -Each flagellum has a basal body, and I could in many instances determine -that it was dumbbell-shaped (Fig. 12). This fact was not always evident, -however, and it was only occasionally that I felt sure of it. Often -the flagella showed only a general thickening within the cells (Fig. -26) while, again, the thickening (basal body) might be quite localized -near the surface of the cell. Each flagellum extends into its cell, -and occasionally I could trace one clear past the nucleus into the -subepithelial nerve-tissue (Fig. 26), just as I did for the axial fibers -of the retinal cells of the simple eyes. In those instances in which I -could do this, the fibers could so clearly be traced that little if any -doubt can exist. I have thus made bold and have drawn the flagella as -continued through their cells into the subepithelial nerve-tissue for all -the cells of the epithelium of Fig. 12. - -A word on the epithelium covering the network cells of Fig. 13. Conant -and Schewiakoff here describe fibers from the supporting lamellæ that -pass in bundles in among the network cells. These fibers are supposed to -be a part of the supporting lamella which reaches out to be a support -for the epithelial cells. (Schewiakoff also describes similar fibers for -other parts of the epithelium.) Now, as Conant himself shows in Fig. -13, these coarse fibers are not of the same consistency and staining -capacity as the supporting lamella. I found them to stain just like the -intracellular parts of the flagella or like the central continuations -of the axial fibers of the cells of the simple eyes. I could, also, -occasionally trace them to the surface of the epithelium, and beyond, -when they became continued as short blunt processes or flagella (Fig. -13). I, therefore, conclude that they are sensory fibers like those I -have described for the other epithelial cells. Yet, that they pass to -the supporting lamella, just as Conant shows in Fig. 13, would seem to -indicate that they are fibers from the supporting lamella or processes of -the epithelial cells. While this stands as an objection to their being -sensory fibers, yet I cannot explain away their being continued distally -as a flagellum, except I assume this continuation to be an artefact. -This does not seem probable. Perhaps they serve both purposes; namely, -that the cell body with its axial fiber is continued to the supporting -lamella, the cell proper ending there, while the axial fiber is continued -as a nerve fiber. I believe this to be the proper explanation. - -The epithelium of the peduncle is quite like the epithelium of the -club just described. Sections through the tips of the epithelial cells -of the peduncle and also sections sagittal to the axis of these cells -give sections like Figs. 25 and 26. I, therefore, conclude that this -epithelium is a sensory flagellate epithelium like that of the clubs. -Nerve tissue and unstriped muscle fibers underly the epithelium of the -peduncles. Claus and Conant also describe a small ventral endodermal -tract of nerve tissue, which according to Conant is connected with the -endodermal nerve tissue found in the region of the radial ganglia. - -To sum up, the epithelium of the club and the peduncle is a flagellate -sensory epithelium whose flagella are continued through the cells as -nerve fibers into the nerve tissue below. _A priori_, judging from the -mass of nerve tissue underlying the epithelium, we should expect the -epithelium to be one strictly sensory. What sense it serves is difficult -to surmise. In the physiological part of this paper I suggested that it -might be tactile, serving in connection with the lithocysts in giving the -animal sensations of space relations. - -Claus mentions having seen patches of flagella on the epithelium of the -clubs. Schewiakoff supposes that his spindle-shaped sensory cells have -only a single flagellum, while his supporting cells have many cilia. -In the latter supposition he was evidently mistaken. Conant (from an -unpublished note) saw the flagella of the epithelium on the living -object and does not think that there could be more than a single one to -each cell. He also concludes from living specimens squeezed out under a -cover-glass, that there is only one kind of cells in the ectoderm. - -Cilia and flagella extending into the cells to which they are attached -are described by a number of observers. - -I shall not endeavor to discuss the subject further, but shall append the -literature on the subject that has come to my notice. (See Literature). -Some of these observers ascribe a nervous function to these centrad -continuations. I am inclined to believe that they represent the primitive -fibrils of Apathy, whether the cilia or flagella are motile or sensory. I -should mention, however, that Apathy has traced the “Primitivfibrillen” -to be continuous with cilia, and also traces them into the sensory rods -of the sensory cells in the sense organs of leeches. Eimer also describes -cilia as continued centrad. - - -_The Network Cells and the Multipolar Ganglion Cells._--Conant is the -first to accurately describe the true structure of the network cells -(Fig. 13) that fill the upper part of the club between the proximal -complex eye and the attachment of the peduncle. I cannot add anything -to Conant’s description. As their name implies, they are filled with -a coarse network-like structure with a central nucleus and nucleolus. -Schewiakoff erroneously described them as ganglion cells and Claus as -supporting cells. I have sometimes thought that they are not made up of -a network, but of a vesicular structure; _i. e._ the network we see is -really produced by the sections of planes that intersect to form little -polyhedral cavities. I could not, however, satisfy myself on this point. -I further saw similar but smaller cells, with a finer network, disposed -in small groups laterally and distally from the attachment of the -peduncle to the club. - -What the function of these network cells is can only be guessed. In size -and shape they somewhat resemble some of the cells found in luminous -organs. Conant, however, nowhere mentions that Charybdea is luminous. - -Lateral to the larger group of network cells lie two groups of large -multipolar ganglion cells (a group on each side). Claus describes these -cells, but Schewiakoff does not specially note them, and evidently -considered them a part of the network cells, which he erroneously -described as ganglion cells. - - -_The Nerve Tissue._--I cannot add anything new on this. It consists of -fine fibers and ganglion cells, quite as described by Claus, Schewiakoff, -and Conant, and fills the club between the ampulla and the epithelium, -except the spaces occupied by the eyes, lithocyst, and network cells. -It is likewise present under the ectoderm of the peduncle, where also -a small tract is found under the endoderm. (See preceding head, or -Claus[3], and Conant[8b]). As already noted, under the distal complex -eye, I find only large nuclei to represent the ganglion cells. By saying -this, however, I do not wish to dispute their ganglionic nature. The -large multipolar ganglion cells I have noted under the preceding topic. - - -_The Supporting Lamella._--The supporting lamella is a continuation, -through the peduncle, of the jelly of the bell. It completely surrounds -the ampulla and the lithocyst, and also forms a partition between them, -so that, as already noted, the lithocyst becomes completely surrounded -by it. It also sends a partition ventrally between the complex eyes -(Figs. 7, 13). Its thickening to form a support for the lens of the -proximal complex eye has already been noticed. I shall limit myself in -the discussion of the supporting lamella to the above short resumé, since -Schewiakoff gives further detail. - - -_The Endothelium of the Ampulla and the “Floating Cells.”_--The ampulla -is lined by a secreting epithelium. This is shown by the large masses -of a secretion within the bases of the cells, and by smaller masses -scattered in the central and more distal parts (Figs. 7, and 27, lower -half). The section of the cells is such in Fig. 7, that the bases of some -(those nearest the supporting lamella) are taken, the central nuclear -region of others, and the tips of those farthest from the supporting -lamella. The section may be said to be taken diagonally through the bases -and central parts of some of the cells, but owing to the curvature of -the ampulla wall, through the tips of others. The secretion is a colloid -substance, staining yellowish gray with iron-hæmatoxylin, blue with Lyons -blue, and reddish with borax-carmine. Sometimes darkly staining rods and -fibers of unknown origin could be seen within the larger masses of the -secretion (Fig. 7). These rods and fibers could also be seen in spaces -within the cells, from which the secretion had evidently been dissolved. -I think there can be no question but that the masses described are a -secretion. Many series, however, do not show it; indeed, an examination -of Conant’s slides gave me little evidence of a secreting function, -though I could demonstrate it in his sections both within the endothelium -and also the floating bodies. The presence or absence of this secretion -is evidently correlated with the feeding habits of the animals, or else -it would be more generally present. - -The endothelium is thickest (the cells are longest) in the upper part -of the ampulla where the supporting lamella approaches the lens of the -proximal complex eye, and in the lower portion of the ampulla (Fig. 7), -in the angle between the concretion cavity and the region of the distal -complex eye. In general, the cells are longest in the upper part of -the ampulla, while in the lower part, especially where they cover the -concretion cavity and the dorsal wall, they may be quite cubical instead -of columnar. Often they present a vacuolated appearance at their bases -(Fig. 27). Claus and Schewiakoff describe and figure this endothelium, -but not in detail. No one, to my knowledge, has described this secretory -function. - -The nuclei of these cells are peculiar. They may contain a network with -a nucleus (Fig. 27). Again, they may show evidence of amitotic division -(Fig. 20, h, i, j). Indeed, Remak’s scheme (Wilson[18] “The Cell,” p. 46) -can be quite readily demonstrated. It is, however, such dumbbell-shaped, -elliptical, or ringed nuclei as seen in Figs. 7 and 20 that are of -special interest. - -I have spoken of some of these nuclei as dumbbell-shaped, elliptical, or -ringed. This is so, however, only in sections. They are really flattened -spheres with a rod of tissue, of the same structure as the nuclear wall, -stretching between the poles. One may conveniently compare the shape of -these nuclei with that of an apple, the core of the apple representing -the rod connecting the two opposite flattened or slightly hollowed poles -of the nucleus. For convenience I shall call the rod connecting the two -poles the axis of the nucleus. The dumbbell or elliptical shape would -be obtained by a meridional section through the axis (Figs. 20, a, b, -c, e, g, k, l, m, n, o, 7). Likewise a ringed appearance with a central -dot would be obtained by a section parallel with the flattened surfaces -or perpendicular to the axis (Figs. 20, d, 7). In a section not strictly -meridional the axis would be cut as in Fig. 29, a, or not show at all. -As nearly as I could determine, the inside of these nuclei is a vacuole, -which the axis penetrates. - -The walls and axis of these nuclei have the structure of a very fine and -dense network that stains very dark with iron-hæmatoxylin. It stains -quite like the reticulum of any nucleus, but is very dense, as though -all the reticulum of the nucleus had been crowded together at the -surface. Judging from appearances like p (Fig. 20), the hollowing out, so -to speak, of these nuclei, would seem to be a process of vacuolation, the -reticulum becoming crowded aside to the surface. But how, on this view, -to amount for the formation of the axis, I do not know. Perhaps the axis -is formed by a pushing in of two opposite poles of a nucleus, the two -invaginations meeting and fusing. On this supposition one might expect -the axis to be hollow (cylindrical), but I could not determine that it -was. Perhaps the centrosphere (or spheres) (see the next paragraph) has -something to do with the formation of the axis (Fig. 20, b, g, e, etc.). - -In the nuclei of Fig. 20 with the dark outlines, and of Fig. 7 a small -reticular body is seen just opposite one end of the axis, or opposite -both ends in g. In d (Fig. 20) this body is seen next the axis just -below (outside) the hollow cup represented by the hollow ring. In this -instance a central granule is seen in the reticular body, as also in -c. I take this reticular body to be the centrosphere, and the central -granule in c and d the centrosome. In k, l, m, n, and o (Fig. 20), which -are from another series, in which the walls of the nuclei did not stain -so dark as in the other nuclei of the same figure, a nucleolus could be -definitely seen, indeed, sometimes quite perched upon the wall of the -nucleus (k, l). In several instances I could see two nuclei, as in o. But -besides these nucleoli, I could in several instances see quite definitely -a reticular body (centrosphere) opposite the axis (m, n, o) quite as I -described for the nuclei with the dark outlines. In a, b, c, d, e and g -the nuclei could not be so readily demonstrated, but I could occasionally -see a darker stained body as in a, c and g, that I have no doubt is the -nucleolus, which here, again, is perched quite upon the surface of the -nucleus. This position of the nucleolus is perhaps due to its having been -crowded to one side by the nucleus becoming hollow. It is no uncommon -thing, either, to find several nuclei in a single cell, sometimes in -process of division or just divided as o and e (Fig. 20), also h, i and -j. The whole nuclear phenomenon that I have described seems to be one of -division. Perhaps it is somehow associated with the giving off of the -secretion of the cells, for these nuclei seem to be found in greatest -abundance in those cells in which the secretion is most abundant. In -Conant’s sections I found but little evidence of these nuclear phenomena -as also little secretion, which all goes to show the association of -the nuclear phenomenon with the secretion. I have failed to find any -descriptions in the literature of nuclei to which I could refer my -observations. - -The endothelium of the ampulla is flagellated (Figs. 7, 17, 27). It -will be seen that there are two slender flagella to a cell. Each pair -of flagella has a pair of basal bodies that are longer than thick, and -which are continued as a thin fiber towards the nucleus of the cell. -That these centrad continuations of the basal bodies extend to or past -the nucleus I could not determine. Sometimes the basal bodies with the -centrad continuations are pushed quite to one side of the cell (Fig. -27), while in other cells they are applied quite to the distal surface -(Figs. 7, 17, 27). Fig. 17, and the part of Fig. 7 that shows these -points, are taken just through the tips of the cells. The darker lines -within the polygonal areas are the intracellular basal bodies with their -centrad continuations, while the thinner lines are the flagella, and -are supposed to lie in the plane just below the plane of the figure. -In those instances in which the centrad continuations are applied to -the distal surface of the cells they could occasionally be seen to bend -centrad (Fig. 27b). While these cilia with their basal bodies and centrad -continuations are usually separate, as shown in the figures, yet they are -at times applied quite closely to each other so that the double nature -of the basal bodies and their centrad continuations is not evident. When -the intracellular continuations of the cilia become pushed to one side or -applied to the distal surface of the cells, I believe this to be due to -the turgor of the cells consequent upon the deposition of large masses -of secretion within them. But I must add that this explanation is not -altogether satisfactory, since in the endoderm cells of the pedalia of -both Charybdea and Tripedalia I found like conditions with no evidence -of a secreting function. (See below, under tentacles.) No one, to my -knowledge, has described the flagellation in detail, although both Claus -and Schewiakoff state that the endoderm is ciliated. - -The “floating cells” in the stomach pockets and in the ampulla, described -by Conant, I believe are in part derived from the endothelial cells of -the ampulla. That a portion of them may arise from the ovary, as Conant -explains, I do not doubt; I have, further, found a mass of floating cells -in a small Charybdea quite as Conant describes for Tripedalia (his Fig. -71). In this Charybdea, however, I could find no traces of any ovary. -Conant speaks of larger and smaller floating cells, and that the smaller -ones are also found in the males. This latter fact agrees with what I -have suggested, that some of the floating cells arise in the ampulla. -My chief reasons for my supposition, however, are the following: I find -globules of the secretion of the ampulla cells in some of the floating -cells and also scattered loosely among them (Fig. 19). These globules -in and among the floating cells have the same general appearance and a -similar staining capacity as the secretion in the ampulla cells. Again, -in spaces within some of the ampulla cells I find bodies resembling -the floating cells with lumps of the secretion within them (Fig. 18). -The conclusion, therefore, lies near that some of the floating cells -originate within the cells of the ampulla, engulf within them some of -the secretion, and are then expelled into the lumen of the ampulla. -Better said, perhaps, they represent portions of the ampulla cells -with some of the secretion. I also found several instances in which a -floating cell had the appearance of being expelled from an ampulla cell. -Conant suggests for a similar observation that the cells were about to -be swallowed by the ampulla cells. I believe, however, that my finding -a secretion similar to that within the cells of the ampulla, in some -of the floating cells, as also bodies very much like them and filled -with secretion within the ampulla cells, together with Conant’s finding -floating cells in males, and finally the observation that the floating -cells are usually quite dilapidated, never showing a healthy cell -structure--all this leads me to conclude that some of the floating cells -originate from the ampulla cells, and that they have a nutrient function -in distributing the secretion. This is quite the reverse of what Conant -supposed,--that they were taken in as nourishment by the ampulla cells. I -also find what appears to be a secretion in the endoderm of the tentacles -of both Charybdea and Tripedalia, and believe this is another source of -the floating cells. (See below, under tentacles.) - -I also found other very darkly staining bodies (Fig. 19) both within -the floating cells and free in the ampulla cavity, and more numerous -in the ampulla cells themselves. This again goes to show that floating -cells take their origin from the ampulla cells. What these darkly -staining bodies are, I cannot say. Perhaps they are something akin to the -“Chromatoider Nebenkörper” described by Lenhossek (L), or they represent -another kind of secretion. If these floating cells are derived from the -cells of the ampulla, the active nuclear division within these also -receives an explanation. Some nuclear matter can usually be observed in -the floating cells. - - -_The Endothelium of the Peduncle._--The endothelium of the peduncle -consists of flagellate columnar cells (Fig. 27, upper half). The cells -are vacuolated at their bases like some of the cells of the ampulla, -and contain a comparatively large nucleus with nucleolus. The flagella -are long and slender, quite like those described for the cells of the -ampulla, except that there is only one to each cell. The basal bodies of -the flagella are of a peculiar shape. They may be described as a bent -spindle, continuous at their distad ends with the cilia and at their -centrad ends with a fiber that can be traced quite to the neighborhood of -the nucleus. I could not trace these fibers into the basal parts of the -cells, except in one instance, and I could not be sure of that (Fig. 27a). - -Another interesting observation in connection with the basal bodies is -that they are bent in one direction on one side of the canal and in -an opposite direction on the other side. In Fig. 27, which represents -a longitudinal section of the endoderm and the supporting lamella of -the dorsal (_i. e._ farthest from the eyes) side of the peduncle, the -distal ends of the basal bodies are bent towards the ampulla, while on -the ventral side they would be bent away from the ampulla. This seems -to suggest that the flagella move the contents of the canal in one -direction on the dorsal side of the canal and in an opposite direction -on the ventral side. Conant observed in living material that bodies in -the ampulla and the canal were moving about, and that bodies within the -tentacles were moving in opposite directions at the same time. This -last observation and the histological facts just described, I believe, -are mutually corroborative. Again, _a priori_, we should expect some -such mechanism as the one described to bring about an exchange between -the contents of the ampulla and that of the stomach pockets. I have not -as yet been able to demonstrate a similar flagellate mechanism in the -tentacles. Flagella and basal bodies are present in the tentacles, but I -could not determine that the basal bodies had any definite arrangement -like that shown in Fig. 27. (See under tentacles.) I may add, yet, that -the cells in the canal of the manubrium have cilia, similar to the ones -just described, with large basal bodies, and with centrad continuations. -Finally, I am not certain but that these cells form buds at their ends -quite like those I describe for the endothelial cells of the tentacles -(see below), and that they aid in the formation of the floating cells. I -thought I saw such buds just at the entrance of the lumen of the peduncle -into the ampulla, but could not find conclusive evidence. - - -_The Tentacles and the Pedalia._--My observations on the tentacles were -begun with the object of demonstrating a flagellate mechanism similar to -the one described above for the endothelium of the peduncle. While I have -failed to demonstrate such a mechanism for the tentacles, yet several -interesting points came to my notice. It will be remembered that the -tentacles of the Cubomedusæ are not directly attached to the bell, but -that a blade-like portion, the pedalium, intervenes between the tentacles -and the bell. For figures of the pedalia and the tentacles the works of -Haake, Claus, Conant and Maas[22] may be consulted. - - -_The Ectoderm._--The ectoderm of the tentacles is the seat of a number of -differentiations. It is quite thick, as the figures (28 and 29) show, and -in this respect is very different from the pedalia, on which the ectoderm -cells are quite cubical. I found evidence of cilia here and there, but -I can add nothing definite about them. Neither can I add any definite -statements regarding the ectoderm cells proper, but what I have to say -relates to their differentiations. - -(a) The _thread cells_ are of two kinds, larger ones and smaller ones. -This is well shown in Fig. 29, which is part of a transverse section of -a tentacle of Tripedalia. Two kinds of nettle-cells are also present -in the tentacles of Charybdea, but they were specially well shown in -Tripedalia. The structure of these thread-cells seems to be typical, and -I have little more to say about them. I wish, however, to call attention -to the five or six unstriped muscle-fibers that are attached to their -basal lateral parts, and which connect them with the basement membrane -(Figs. 28, 29). Claus describes these muscle-fibers and mentions that Fr. -Müller has described them before him, but I have not found them mentioned -elsewhere in the literature of nettle-cells. Professor Brooks tells me, -however, that he has often found them. It would appear from Fig. 29 that -they serve to retract the thread-cells from the surface. Claus suggests -that the muscles are developed from the cnidoblasts. - -(b) The plain subectodermal _muscle-fibers_ are of interest. In -Charybdea they lie wholly enclosed within canals of the supporting -lamella (Fig. 32, upper part). They run longitudinally, and near the -base of each tentacle pass out of their canals and become strictly -subectodermal (Figs. 31, 32). This is for Charybdea. In Tripedalia they -rarely come to lie in closed canals as in Charybdea. These facts show -beyond doubt that these muscles are developed from the ectoderm. Claus -has suggested their ectodermal origin, but did not demonstrate it. He -also suggested that they become inclosed in canals by the supporting -lamella pushing up around them and finally fusing above them. This, I -believe, is demonstrated by the conditions in Tripedalia (Fig. 29). Here -the canals usually remain open, but occasionally, as in the left-hand -canal, one may become completely inclosed. This condition of things -suggests the intra-lamellar muscles found in actiniarians. The nuclei -found in the canals with the muscle-fibers probably belong to the cells -from which the muscles become differentiated. Claus figures these -muscle-fibers and nuclei, and it may be added that the supporting lamella -he figures, for C. marsupialis, is much thicker than I have figured it -for C. Xaymacana and Tripedalia cystophora. The number of muscle-canals -also is greater and occupies a much greater depth of the thickness of -the lamella. Since Claus gives a figure of a transverse section showing -the muscles in their enclosed canals, I have not deemed it necessary to -duplicate his figure. In the transition from a tentacle to a pedalium, -the muscles are most strongly developed toward and at the edges of the -pedalium. This is true for the pedalia in general, and accounts for -the readiness with which they can be bent inwards, as noted in the -physiological part of this paper. - -(c) I have found a single _ganglion-cell_ among the cells of the ectoderm -of the tentacles. This showed so plainly that I have figured it (Fig. -28). Other ganglion-cells no doubt exist, but could probably not be -distinguished from other cells. In its position in Fig. 28 it appears to -be associated with the nettle-cell shown just above it. Its position is -very much the same as that figured by Lendenfeld (25a). - - -_The Endoderm._--The cells of the endoderm of a tentacle are long and -quite slender (Fig. 31). At their bases they are vacuolated quite like -the cells of the ampulla and the canal of the sensory clubs. They contain -a well-formed nucleus with a nucleolus. In their distal half small light -bodies with a dark center are very evident. These bodies are evidently a -secretion. - -Another peculiar phenomenon presents itself in these cells. The distal -part of each cell becomes separated off from its body by what appears -to be the formation of a transverse cell-wall (Fig. 31, c-d). I have -found the ends of these cells quite separated off in some series. The -formation of the walls seems to begin as a thickening at the sides of the -cells, and a section through this region, transverse to the cells, would -appear like Fig. 30. The dots in the centers of the polygonal areas of -this figure are the centrad continuations of the cilia to be described -below. As already remarked in describing the endoderm of the ampulla, I -believe we here have another place of origin of the “floating cells.” The -secretion just described moves into the distal parts of the cells prior -to their separation (Fig. 31). In some series I could see these secretion -bodies much more numerous within the distal ends of the cells than in -Fig. 31. - -As will be seen in Fig. 31, each of the endoderm cells of the tentacles -has a flagellum that extends into the lumen of the tentacle. Each -flagellum has a thickening just within its cell, which may be regarded -as a basal body. From this basal body, again, a small fiber extends -centrad into each cell. It does not appear that the flagella are thrown -off with the distal parts of the cells; at all events, I never found -them connected with any of the floating cells except in a few doubtful -instances. - -What I have said for the endoderm of the tentacle of Charybdea applies -equally to Tripedalia. - -Claus, in his figure of a transverse section of a tentacle of C. -marsupialis shows the endoderm as cubical. I cannot explain why there -should be such a difference between the endoderm of the tentacles of _C. -marsupialis_ and that of the tentacles of _C. Xaymacana_ and _Tripedalia -cystophora_. Claus does not describe the endoderm in detail. - -The endoderm cells of the pedalia of both Charybdea and Tripedalia are -cubical and possess flagella, basal bodies, and centrad continuations, -quite like those I have described for the endoderm cells of the ampulla. -The double nature of the basal bodies and the centrad continuations is, -however, not so evident. A secretion I did not find. Histologically, -therefore, the endothelium of the pedalia corresponds rather with that of -the ampulla, and that of the tentacles with that of the peduncle of the -clubs. - - -SUMMARY. - -The most important results in the histological part of this paper relate -to the structure of the retinas of the eyes of the sensory clubs. - -The retina of the distal complex eye is composed of three kinds of cells: -two kinds of sensory cells (the prism and pyramid cells), and the long -pigment cells (Figs. 1-9). The prism and pyramid cells have each an axial -nerve fiber in their prisms and pyramids respectively. These fibers I -could, however, trace only to the neighborhood of the nuclei. But since -I could trace similar fibers in the retinal cells of the simple eyes -(Fig. 16) past the nucleus into the subretinal nerve tissue, I believe -that the axial fibers in question also extend centrad as nerve fibers -into the subretinal nerve tissue. Other observers also figure such fibers -as extending centrad as nerve fibers. The axial fibers of the prism -cells have each a dumbbell-shaped basal body at their entrance into the -pigmented part of a cell. The evidence for a body of such shape in the -pyramid cells was not conclusive, though a basal body for the axial fiber -exists. The long pigment cells project or retract their pigment in light -or darkness respectively and thus seem to serve to check the diffusion of -light in the retina. I have also supposed that these cells may serve for -conducting impulses to the lens, and that the latter is adjustable. - -The proximal complex eye (Fig. 13) has only the prism cells present in -its retina, and not two kinds of cells as Schewiakoff has described (see -text, pp. 53, 60, 63) for all the eyes. - -The simple eyes (Fig. 12), two on each side of a club, four in all, -also have only one kind of cells in their retinas, and each cell has -a flagellum extending into the vitreous secretion of the lumen. These -flagella could be traced centrad as a nerve fiber (Figs. 12, 16). -Similarly, a nerve fiber could be traced centrad from the flagella of -the epithelial cells of the clubs. Dumbbell-shaped basal bodies for the -flagella of the simple eyes could also be demonstrated, but the evidence -for this in the epithelial cells of the clubs was not so satisfactory. - -Other points of interest are: A secretory epithelium lining the ampulla -of the clubs, and a somewhat similar epithelium lining the canals of -the tentacles (Figs. 7, 27, 31); the partial origin of the “floating -bodies” in the canals of the clubs and tentacles and the stomach pockets -from these epithelia (Figs. 18, 19); two flagella to each cell of -the endothelium of the ampulla and of the pedalia (Figs. 7, 17); the -peculiar nuclei in the endothelial cells of the ampulla (Fig. 20); the -longitudinal muscles of the tentacles being completely inclosed within -canals of the supporting lamella, but near the base of a tentacle -becoming subectodermal. This demonstrates their ectodermal origin. In -Tripedalia it is seldom that any of these muscles become enclosed as in -Charybdea (Fig. 29). - -If to the reader my results seem to embody a somewhat heterogeneous -detail, he must remember that the work consists partly in corroborating -and partly in supplementing the work of previous observers, and that, -in general, histological detail does not usually make the most readable -paper. - -BIOLOGICAL LABORATORY, JOHNS HOPKINS UNIV., May 1899. - - - - -FOOTNOTES - - -[a] It was at one time supposed that the concretions in the marginal -bodies of medusæ represented lenses and the surrounding nerve tissue the -optic nerve, a supposition so highly improbable that it never gained any -acceptance. (Ib., p. 41, note.) - -[b] Eimer’s results I get from Romanes and Hesse[III]. - -[c] By no means do I wish to attribute intelligence to these animals. - -[d] Haake[2] says that in the adult _Charybdea Rostonii_ the vitreous -bodies of the complex eyes are absent but present in the young. It is -difficult to explain this observation except on grounds of imperfect -preservation of the adult material, for in all observations on other -forms a vitreous body is described. Haake evidently did not use sections, -and for this reason his results must be regarded as of doubtful accuracy. -Haake also says that the simple lateral eyes of the clubs are absent in -the adult, but present in the young. - -[e] In the series from which Fig. 3 is taken the pyramid-cells are not -so readily demonstrated. Indeed, I missed them altogether at first in -this and some other series and supposed that there were only two kinds of -cells (19), but upon a careful re-examination I could demonstrate them to -my satisfaction. They did not show, however, in the particular section of -Fig. 3, so that they are not indicated in this figure. - -[f] I go into this at some length because the cell-walls in the series -that showed the nuclei best differentiated as lighter and darker ones did -not show well, and there might be some doubt that these lighter nuclei -belonged to the pyramid cells. I could, however, in many instances, -trace the axial fibers of the pyramids through the pigmented zone to -these lighter nuclei (as already noted) which fact can leave no doubt -but that some of these nuclei belong to the pyramid cells. (Similar -nuclei, however, are found to belong to the long pigment cells, to be -described below.) Centrad these pyramid cells are continued into a single -process just as the prism cells were shown to be (Fig. 7). Figures 6, -8, 9, and 21 show samples of all the pigmented cells found in macerated -preparations, and none of these (except Fig. 9, long pigment cells) show -more than a single centrad process. Hence, I conclude that centrad both -the pyramid cells and prism cells are continued as a single prolongation. - -[g] I have been able to demonstrate nucleoli in all the different nuclei -of the cells of the sensory clubs. - -[h] It may be objected that my criterion, the presence of axial fibers, -is not necessarily characteristic of visual cells. However, the great -general occurrence of such axial fibers (Patten,[5] Grenacher,[16] -Schreiner,[12] Hesse,[13] myself, in simple complex eye, see below, and -perhaps others) in eyes in which the retina has only one kind of cells, -would seem to indicate that they are quite characteristic of visual -cells. Note again that in the proximal eye of Charybdea there is only one -kind of cells and with axial fibers. - -[i] Mr. J. C. Olsen, of the Chemical Laboratory, kindly made these tests -for me. - - - - -LITERATURE. - - -LITERATURE REFERRED TO IN THE SECTION ON PHYSIOLOGY. - -I. ROMANES, G. J. a. ’75, ’77. The Locomotor System of Medusæ. -Philosophical Transactions. London. Vol. CLXVI, pt. 1. Vol. CLXVII, pt. 2. - - b. ’85. Jelly-fish, Star-fish and Sea-urchins. London. - -II. MURBACH, LOUIS. ’95. Preliminary Notes on the Life-history of -Gonionemus. Journal of Morphology. Vol. XI. - -III. HESSE, R. ’95. Über das Nervensystem und die Sinnesorgane v. -Rhizostoma Cuvieri. Zeit. Wis. Zool., B. LX. - -IV. EIMER, TH. Zoologische Untersuchungen. ’74. Würzburg Verhandlungen. -VI. Bd. - -V. HAECKEL, E. ’79. Monographie der Medusen. Jena. - -VI. BERGER, E. W. ’98. Abstract of Dr. F. S. Conant’s Notes on the -Physiology of the Medusæ. Johns Hopkins University Circulars. Vol. XVIII, -No. 137. - -VII. (See also 8, below.) - - -LITERATURE REFERRED TO IN THE SECTION ON HISTOLOGY. - -1. CARRIÈRE, J. ’85. Die Schorgane der Thiere. München u. Leipzig. - -2. HAAKE, W. ’87. Scyphomedusen des St. Vincent Golfes. Jen. Zeit. f. -Naturwis., Bd. XX., pp. 596-597, 602-604. - -3. CLAUS, C. ’78. Über Charybdea marsupialis. Arb. aus dem Zool., Inst. -Univers. Wien., Bd. I. - -4. SCHEWIAKOFF, W. ’89. Beiträge zur Kenntniss des Acalephenauges. Morph. -Jahrb., Bd. XV, H. 1. - -5. PATTEN, WILLIAM. a. ’89. Studies on the eyes of Arthropods. II. Eyes -of Acilius. Journal of Morphology. Vol. II. - - b. ’98. A Basis for a Theory of Color Vision. American - Naturalist. Vol. XXXII, No. 383. - -6. APATHY, ST. ’97. Das Leitende Element des Nervensystems u. seine -topographischen Beziehungen zu den Zellen. Mitt. Zool. Stat. Neapel., Bd. -XII, H. 4. - -7. PARKER, G. H. ’97. Photomechanical Changes in the Retinal Pigment -Cells of Palæmonites, and their Relation to the Central Nervous System. -Bull. Mus. Comp. Zool. Harvard Coll. Vol. XXX, No. 6. - -8. CONANT, F. S. a. ’97. Notes on the Cubomedusæ. Johns Hopkins -University Circulars. Vol. XVII, No. 132. - - b. ’98. The Cubomedusæ. Memoirs Biological Laboratory Johns - Hopkins Univ. Vol. IV, No. 1. - -9. A REVIEW OF 5b. ’99. A Theory of Color Vision. Natural Science. Vol. -XIV, No. 85. - -10. HERRICK, F. H. ’91. The Embryology and Metamorphosis of the Macroura -(Brooks and Herrick). Natl. Acad. Sciences. Vol. V, p. 454. - -11. HERTWIG, O. & R. ’78. Das Nervensystem und die Sinnesorgane der -Medusen. Leipzig. - -12. SCHREINER, K. E. a. ’96. Die Augen bei Pecten und Lima. Bergens -Museums Aarbog. - - b. ’97. Histologische Studien über die Augen der freilebenden - marinen Borstenwürmer. Bergens Museums Aarbog. - -13. HESSE, R. ’99. Untersuchungen über die Organe der Lichtempfindung -bei niederen Thieren. V. Die Augen der Polychäten Anneliden. Zeit. Wis. -Zool., B. LXV, H. 3. - -14. ANDREWS, E. A. ’92. On the Eyes of Polychætous Annelids. Journal of -Morphology. Vol. VII. - -15. WILSON, H. V. ’78. Unpublished Notes. - -16. GRENACHER, H. ’84. Abhandlungen zur vergleichenden Anatomie des -Auges. I. Die Retine der Cephalopoden. Abhandl. der Naturf. Gesellsch. zu -Halle. Bd. XVI. - -17. BEER, THEODORE. ’98. Die Accomodation des Auges in der Thierreihe. -Wiener klinische Wochenschrift. Nr. 42. - -18. WILSON, E. B. ’96. The Cell. - -19. BERGER, E. W. ’98. The Histological Structure of the Eyes of -Cubomedusæ. The Journal of Comp. Neurology. Vol. VIII, No. 3. - -20. LENDENFELD, R. Die Nesselzellen der Chidarier. (Review and -bibliography.) Biol. Centralbl. Bd. XVII, Nr. 13. - -21. SCHNEIDER, K. ’90. Histologie von Hydra fusca mit besonderer -Berücksichtigung des Nervensystems der Hydropolypen. Arch. Mik. Anat. -Vol. XXXV. - -22. MAAS, O. ’98. Die Medusen. (Charybdea arborifera, Systematic.) Mem. -Mus. Comp. Zool., Harvard Coll. Vol. XXIII, No. 1. - - -LITERATURE REFERRING TO THE CENTRAD CONTINUATIONS OF CILIA AND FLAGELLA. - -A. HAECKEL, E. ’72. Die Kalkschwämme. Vol. I, p. 141; Vol. III, Pl. 25, -Figs. 3-5. - -B. SCHULTZE, F. E. ’75. Rhizopodien Studien. V. Arch. Mik. Anat. Bd. II, -p. 583. - -C. EIMER, TH. ’77. Weitere Nachrichten über d. Bau des Zellkerns, nebst -Bemerkungen über Wimperepithelien. Arch. f. Mik. Anat. Bd. XIV, Taf. VII, -p. 114. - -D. BÜTSCHLI, O. ’78. Beiträge zur Kenntniss der Flagellaten, u. s. w. -Zeit. f. Wis. Zool. Bd. XXX, p. 269. - -E. ENGELMANN, TH. W. ’80. Zur Anatomie u. Physiologie d. Flimmerzellen -Pflüger’s Arch. Bd. XXIII. - -F. HATSCHEK, B. ’85. Entwickelung der Trochophora von Eupomatus uncinatus -Arb. Zool. Inst. Wien., Bd. VI, p. 139. - -G. HEIDER, K. ’86. Zur Metamorphose der Oscarella lobularis. Arb. Zool. -Inst. Wien., Bd. VI, pp. 189-194. - -H. SCHNEIDER, K. C. ’92. Einige histologische Befunde an Coelenterata. -Jen. Zeit. f. Nat. 27, N. F. 20. - -I. HECHT, EMILE. ’95. Contribution a l’Étude des Nudibranchs. Memoirs de -la Société Zool. de France. T. 8, Pl. IV, Fig. 45. - -J. MINCHIN, E. A. ’96. Notes on the Larva and Postlarval Development of -Leucolosolemia variabilis, etc. Proc. R. Soc., London. Vol. LX. - -K. HENNEGUY, L. F. ’98. Sur le rapports des ciles vibrales avec les -centrosomes. Arch. d’anat. micros., T. 1. - -L. LENHOSSEK, H. ’98. Über Flimmerzellen. Anat. Anz. (Supplement.) Bd. -XIV. - -M. PETRE, CARL. ’99. Das Centrum für die Flimmer u. Geisel-bewegung. -Anat. Anz. Bd. XV, Nos. 14 and 15. - -N. See also 6. - - -REFERENCE LETTERS. - - a = flagellum in Fig. 27, that is supposed to extend centrad - beyond the nucleus. - - b = twin flagella in Fig. 27, of which the centrad continuation is - seen applied against the distal surface of the cells and to - be continued centrad. - - c = capsule of lens. - - cf = axial fibers of cells extending centrad. - - co = cornea. - - concr = concretion cavity. - - ec = ectoderm. - - en = endoderm. - - f = flagella. - - flp = distal fiber of a long pigment cell. - - fpr = axial nerve fiber of a prism cell. - - fpyr = axial nerve fiber of a pyramid cell. - - frc = axial nerve fiber of the retinal cells of the simple eyes. - - gc = ganglion cells. - - ind = impression of the lens probably due to the pressure of weight - against the surrounding tissue. - - l = lens. - - lp = long pigment cells. - - m = muscle fibers. - - namp = nuclei of ampulla cells. - - nc = network cells (Figs. 13 and 16), and nettle cells (Figs. - 28, 29). - - nf = nerve fibers and tissue. - - nlp = nucleus of long pigment cell. - - nm = nucleus of muscle cells. - - nprc = nucleus of prism cell. - - npyrc = nucleus of pyramid cell. - - nz = nuclear zone. - - pr = prism of prism cell. - - prc = prism cell. - - pyr = pyramid of pyramid cell. - - pyrc = pyramid cell. - - pz = pigmented zone. - - r = retina. - - s = secretion in endo. of tent. and ampulla. - - sh = shrinkage space. - - sec = vitreous secretion in the lumen of the simple eyes. - - sla = supporting lamella. - - vb = vitreous body or zone. - - x = (1) the approximate level at which Fig. 4 should be cut - transversely to give Figs. 1 and 3. - - (2) the thickening of the supporting lamella in Fig. 13 to - support the lens. - - * = Point of approximation of cells of lenses in Figs. 7 and 13. - - - - -DESCRIPTION OF FIGURES. - -ALL FIGURES, UNLESS OTHERWISE STATED, ARE FROM CHARYBDEA. - - -Fig. 1. This figure represents a transverse section through a portion -of the vitreous body of the distal complex eye at about the level x of -Fig. 4. Three kinds of areas are seen, namely, the prisms and pyramids -with their axial fibers and the distal continuations of the long pigment -cells. Towards the lower left of the figure the section is a little more -distal than at the right and the transverse areas of the long pigment -cells are no more so large as at the right of the figure. The dark -granules in the areas of the long pigment cells represent pigment. Camera -lucida sketch. ×920. pp. 45, 46, 48, 49, 50, 51, 52, 54. - -Fig. 2. This figure is a camera lucida sketch from a section taken -transverse through the most distal part of the pigmented zone of a -slightly pigmented retina of a distal complex eye. The presence of three -kinds of elements is again evident. The dots without the polygonal areas -represent the centrad continuations of the axial fibers of the prism -cells. The lettering explains the other areas. ×920. pp. 46, 48, 50. - -Fig. 3. This is from a section similar to that of Fig. 1, but a little -more distal. At the right, the section is more distal than at the left -of the figure, in consequence of which the long pigment cells are there -taken through their distal fibers. Note the small shrinkage spaces about -the axial fibers of the prisms. The white lines bounding the prism areas -appear as in nature. The pyramid cells are not shown in this figure. -×950. Camera sketch. pp. 50, 51, 52, 54. - -Fig. 4. This figure is from a section taken parallel to the long axis -of the cells of the retina of a distal complex eye. It is from a camera -sketch, and nothing has been put into the figure except what could be -clearly seen. The lateral boundary lines of the prisms are not shown. -Note the evidence for the existence of three kinds of cells. ×920. pp. -44-52, 54. - -Fig. 5. This figure represents a sagittal section through the nuclear and -pigmented zones and the subretinal nerve tissue of a slightly pigmented -retina of a distal complex eye, that had been killed in the dark. Camera -sketch. The pyramid cells are not shown. ×900. pp. 47, 51, 52, 53. - -Fig. 6. These cells are from a preparation by Conant of a sensory club, -macerated in acetic acid. Cell a is evidently an iris cell. The others -are probably prism cells from the proximal complex eye. ×900. pp. 44, 48. - -Fig. 7. In this figure I represent a sagittal section through the -distal complex eye. In the middle half of the section, the nuclei, the -prism and pyramid cells with their axial fibers, and the long pigment -cells with their large distal fibers are all strictly camera lucida -sketched. A portion of the pigmented zone has been left unpigmented to -better show its structure. At the right and above the concretion cavity -is shown a portion of the endoderm of the ampulla. The section is not -strictly in a dorsoventral plane of the club, in consequence of which -the cells of the ampulla are cut diagonally and through their tips. Note -the dumbbell-shaped nuclei of the ampulla cells, as also the masses of -secretion. A part of the retina of the proximal complex eye is shown in -the upper part of the figure. ×920. pp. 41-54, 63, 64, 68-71. - -Fig. 8. These cells are from a macerated preparation. Cells a, b, c, d -may be either prism or pyramid cells from the distal complex eye or prism -cells from the proximal complex eye. Cells e and f are probably from the -right fourth (Fig. 13) of the retina of the proximal complex eye or from -the simple eyes. The unlettered cells are probably from the simple eyes. -Some of these show a distal process. ×900. pp. 48, 62, 65. - -Fig. 9. The cells here figured are long pigment cells from the same -preparation as Fig. 6. ×900. pp. 50, 51. - -Fig. 10. This drawing shows an end view of a group of prisms from the -same preparation as Fig. 6. ×900. pp. 46. - -Fig. 11. This group of prisms are from the same preparation as Fig. 6. -Two of them are broken off. The fibers seen at the lower end are probably -some of the axial fibers. The fiber at the upper end I believe is -interprismatic and the distal fiber of a long pigment cell. ×900. pp. 46. - -Fig. 12. This figure is a summary of my results on the simple eyes. -It is from a camera sketch of one of the distal eyes, but somewhat -diagrammatic. The left side of the figure is proximal, the right side -distal. ×920. pp. 61, 62, 64, 65. - -Fig. 13. Sagittal dorsoventral section of a proximal complex eye. Conant -drew and published this as his Fig. 69. Conant’s evidence regarding -the axial fibers of the prism cells was incomplete; so that, in this -respect, he left his figure unfinished. I have drawn in these fibers and -republish the figure. At the right of the retina and next the lens (the -white space) the vitreous body is incomplete and the fibers from the -retinal cells project freely into the space. This part of the retina also -remains unpigmented. Like my Fig. 7, this figure evidently represents -a section somewhat to one side of a sagittal dorsoventral plane of the -club, so that the endoderm cells of the ampulla are cut diagonally or -transversely. pp. 41-44, 60, 64-68. - -Fig. 14. This is drawn to show how regularly small shrinkage spaces may -occur in transverse sections of the vitreous bodies. This figure is from -a transverse section of the vitreous body of a proximal complex eye. -I believe that these spaces are determined by the axial fibers of the -prisms. Prism outlines are not shown. ×950. pp. 54. - -Fig. 15. This figure is a drawing of a portion of a transverse section of -one of the simple eyes. Note the flagella from the retinal cells. pp. 62. - -Fig. 16. The section of the lower left hand corner of this figure is -through a portion of one of the proximal complex eyes, and shows the -centrad continuation of the axial nerve fibers of the retinal cells. The -section is such, that, besides the simple eye, the nuclei of the proximal -complex eye (upper part of figure) and two network cells are cut. ×920. -pp. 47, 62, 63. - -Fig. 17. A transverse section through the tips of the ampulla cells is -here shown. To the left is towards the upper end of the ampulla. The -basal bodies with the centrad fibers are in the plane of the section, -while the flagella are supposed to extend below the plane of the section. -×1350. pp. 71. - -Fig. 18. These bodies, from within the ampulla cells, contain some of -the secretion of the ampulla cells, and resemble the “floating bodies.” -×1350. pp. 72. - -Fig. 19. The “floating bodies” here represented are from the ampulla. -Globules of a secretion similar to that found in the ampulla cells are -seen both within and without the bodies. Note also the two black bodies -without the cells and two or three similar ones within the cells. These -latter bodies are of doubtful nature. ×1320. pp. 72. - -Fig. 20. This figure represents sections of the various nuclei found -within the ampulla cells. ×1350. pp. 69, 70. - -Fig. 21. These cells are from the same preparation as Fig. 6. They are -evidently retinal cells from the simple eyes. The tendency of their -pigmented ends to become globular, I believe, is due to their having -become isolated before they hardened during maceration. ×920. pp. 62. - -Fig. 22. This diagram illustrates the retraction of the long pigment -cells. The dotted lines in the vitreous body mark the outlines of the -prisms, while the continuous lines represent the axial fibers of the -prism and pyramid cells. pp. 45, 46, 48, 49, 53. - -Fig. 23. These cells are from the epithelium of a sensory club. They are -from the same preparation as Fig. 6. Flagella are not shown. ×900. p. 64. - -Fig. 24. This group of epithelial cells of a club are from the same -preparation as Fig. 6. ×850. p. 64. - -Fig. 25. This sketch is a transverse section through the tips of the -epithelial cells of a club. The polygonal areas are the cells, while the -central dots are the centrad continuations (nerve fibers) the flagella of -the cells. ×920. pp. 63, 65, 66. - -Fig. 26. The flagella of the epithelium of a club are in this figure seen -to extend centrad, some beyond the nuclei. Cell outlines are not shown. -×920. pp. 64, 65, 66. - -Fig. 27. The cells of the lower half of this figure belong to the -ampulla, those of the upper half to the canal of the peduncle. The right -side of the figure is towards the eyes (the ventral side) of the club. -Globules of secretion are seen within the ampulla cells, as also a -globule without. The ring above the latter globule is probably an empty -shell of a floating cell. ×1320. pp. 68, 69, 71, 73. - -Fig. 28. This figure is from a transverse section of a tentacle of -Charybdea. The mass with darkly stained granules is the remains of a -thread cell. The ectoderm and a small part of the supporting lamella only -are figured. Note the large ganglion cell. ×920. pp. 74, 75. - -Fig. 29. Part of a transverse section of a tentacle of Tripedalia. -The endoderm is not figured. The supporting lamella is seen to be -considerably thinner than in Charybdea. Note the subectodermal muscles, -as also the muscle fibers to the thread cells. ×920. pp. 69, 74, 75. - -Fig. 30. This is a transverse section through the endothelium of a -tentacle of Charybdea in the line c d of Fig. 32. The dark lines bounding -the polygonal areas are the thickenings of the sides of the walls of -the cells in the line indicated. The central dots are the centrad -continuations of the flagella. ×920. p. 76. - -Fig. 31. This figure is a transverse section through a tentacle of -Charybdea at about the middle of Fig. 32, _i. e._ so near to where the -tentacle joins the pedalium, that the muscles within the lamella have all -come to lie under the ectoderm. The ectoderm is not shown. ×920. pp. 75, -76. - -Fig. 32. A longitudinal section through the supporting lamella only, of -a tentacle of Charybdea, is here shown. In the upper part of the figure -the muscle fibers are seen wholly enclosed by the supporting lamella. In -the middle of the figure they are seen to pass out of their canal. In the -lower part of the figure, the supporting lamella is seen to bend to the -right where it becomes continuous with the lamella of the pedalium. ×920. -p. 75. - -[Illustration: CUBOMEDUSÆ. PLATE I. - -E. W. Berger, del.] - -[Illustration: CUBOMEDUSÆ. PLATE II. - -E. W. Berger, del.] - -[Illustration: CUBOMEDUSÆ. PLATE III. - -E. W. Berger, del. 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